Flow regulated pressure swing adsorption system

ABSTRACT

Pressure swing adsorption (PSA) separation of a gas mixture is performed in an apparatus with a plurality of adsorbent beds. The invention provides rotary multiport distributor valves to control the timing sequence of the PSA cycle steps between the beds, with flow controls cooperating with the rotary distributor valves to control the volume rates of gas flows to and from the adsorbent beds in blowdown, purge, equalization and repressurization steps.

The present application is a continuation of co-pending U.S. Reissuepatent application No. 10/150,784, entitled “Flow Regulated PressureSwing Adsorption System,” filed on May 16, 2002, and to be issued asU.S. Pat. No. RE38,493 on Apr. 13, 2004, which is a reissue of U.S.patent application No. 08/637,176, entitled “Flow Regulated PressureSwing Adsorption System,” filed Apr. 24, 1996, now U.S. Pat. No.6,063,161, the disclosures of which are hereby incorporated byreference.

TECHNICAL FIELD

The invention relates to separations conducted by pressure swingadsorption (PSA). The present invention provides simplified controls,with enhanced flexibility of control adjustment through flow regulationunder changing operating conditions.

BACKGROUND ART

Gas separation by pressure swing adsorption is achieved by coordinatedpressure cycling and flow reversals over adsorbent beds whichpreferentially adsorb a more readily adsorbed component relative to aless readily adsorbed component of the mixture. The total pressure iselevated to a higher pressure during intervals of flow in a firstdirection through the adsorbent bed, and is reduced to a lower pressureduring intervals of flow in the reverse direction. As the cycle isrepeated, the less readily adsorbed or “light” component is concentratedin the first direction, while the more readily adsorbed or “heavy”component is concentrated in the reverse direction.

The conventional process for gas separation by pressure swing adsorptionuses two or more adsorbent beds in parallel, with directional valves ateach end of each adsorbent bed to connect the beds in alternatingsequence to pressure sources and sinks, thus establishing the changes ofworking pressure and flow direction. Valves are required to control feedgas admission and discharge of gas enriched in the heavy component atthe feed ends of the adsorbent beds, to control delivery of gas enrichedin the light component at the product ends of the adsorbent beds, and tocontrol depressurization and repressurization steps from either the feedor product ends of the beds.

Enhanced separation performance is achieved in well known PSA cyclesusing steps for each adsorbent bed of cocurrent feed at the higher cyclepressure, cocurrent initial blowdown, countercurrent final blowdown,countercurrent purge at the lower cycle pressure, and countercurrentpressurization. As disclosed by Kiyonaga (U.S. Pat. No. 3,176,444),Wagner (U.S. Pat. No. 3,430,418) and Fuderer et al (U.S. Pat. No.3,986,849), improved product recovery can be obtained with more than twoadsorbent beds operating in parallel, by performing pressureequalization steps between the separate beds so that a first bedundergoing a pressure reduction step exchanges gas which typically hasbeen substantially purified to a second bed undergoing a pressureincrease step so that the working pressure of the first and second bedsis equalized to a pressure intermediate between the high and lowpressures of the cycle.

With a greater number of beds, multiple pressure equalization steps canbe achieved, although the valve logic and controls are then greatlycomplicated. Modern industrial scale PSA plants with six or more beds(e.g. as described by Fuderer et al for hydrogen purification) use alarge number of two-way valves under computer control to establish boththe cycle switching logic and adaptive flow control of each step.

It is well known that the complexity of valving in PSA systems may bereduced by use of multiport valves to establish the cycle switchinglogic. Thus, Synder (U.S. Pat. No. 4,272,265) has disclosed a rotarydistributor valve for controlling high pressure feed and low pressureexhaust flows for an air separation pressure swing adsorption systemwith multiple beds. Use of a coaxially aligned pair of distributorvalves, respectively controlling feed and product gas flows at oppositeends of the beds, was disclosed by van Weenen (U.S. Pat. No. 4,469,494),Hill (U.S. Pat. No. 5,112,367) and Hill et al (U.S. Pat. Nos. 5,268,021and 5,366,541) have disclosed oxygen concentration PSA devices usingmultiport rotary valves with stationary adsorbent beds. The processesdisclosed by van Weenan and Hill have pressure equalization stepsconducted at respectively the product or feed ends of the adsorbentbeds.

Prior art PSA systems with multiport distributor valves have been usedcommercially in small scale oxygen enrichment applications, asrecommended by Dangieri et al (U.S. Pat. No. 4,406,675) for a rapid PSAprocess in which flow control is intentionally established by relativelysteep pressure gradients in the adsorbent bed. The adsorbent bed musttherefore be spring-loaded or otherwise immobilized to preventattritional damage.

For large industrial PSA systems, mechanical immobilization of theadsorbent beds has not been practicable. Careful flow control isrequired to ensure that pressure gradients in the adsorbent bed are keptlow, well below the onset of fluidization.

Mattia (U.S. Pat. No. 4,452,612) and Boudet et al (U.S. Pat. No.5,133,784) disclose PSA devices using a rotary adsorbent bedconfiguration. The multiple adsorbent bed ports of an adsorbent bedrotor sweep past fixed ports for feed admission, product delivery andpressure equalization; with the relative rotation of the ports providingthe function of a rotary distributor valve. Related devices aredisclosed by Kagimoto et al (U.S. Pat. No. 5,248,325). All of theseprior art devices use multiple adsorbent beds in parallel and operatingsequentially on the same cycle, with multiport distributor rotary valvesfor controlling gas flows to, from and between the adsorbent beds.

An advantage of PSA devices with the adsorbent beds mounted on a rotaryadsorbent bed assembly, as in the cited prior art inventions by Mattiaand Boudet et al., is that function port connections for feed, exhaust,product and pressure equalization are made to the stator and are thusaccessible to flow control devices. However, a rotary adsorbent bedassembly may be impracticable for large PSA units, owing to the weightof the rotating assembly. Also, when separating gas components which arehighly inflammable or toxic, the rotary adsorbent bed assembly wouldneed to be completely enclosed in a containment shroud to capture anyleakage from large diameter rotary seals. Hence, PSA devices withstationary adsorbent beds will be preferred for larger scale systems,and for applications processing hazardous gases such as hydrogen.

In some of the above referenced prior art (e.g. Mattia, Boudet, and vanWeenan), the rotary distributor valve would rotate continuously. Lywood(U.S. Pat. No. 4,758,253) and Kai et al (U.S. Pat. No. 5,256,174) havementioned intermittent actuation of rotary multiport distributor valvesfor PSA systems, so that the distributor valve is stopped at a fullyopen position during each step of the cycle, and the distributor valveis then switched quickly to its next fully open position for the nextstep of the cycle.

It will be apparent that the multiport valves disclosed in the abovecited inventions enable a simplification of PSA cycle switching logic,particularly those using multiple beds with pressure equalization steps,since the control functions of a multiplicity of two-way valves areconsolidated into one or two multiport distributor valves. However,these prior art devices have limited utility except in small scaleapplications, owing to their lack of control flexibility. Since valvetiming logic and port orifice sizing of the multiport valves are fixedrigidly in these prior art inventions, there is no provision for flowcontrol to provide operational adjustment under changing feed conditionsor during intervals of reduced product demand, or for performanceoptimization.

This inflexibility of control is most limiting for those of the citedprior art inventions which use multiport valves to exchange gas betweena pair of beds, and across a pressure difference between that pair ofbeds. Such gas exchanges between pairs of beds arise in pressureequalization steps, in purge steps, and in product repressurizationsteps. For the PSA cycle to operate properly in a given applicationbetween given high and low pressures of the cycle, a correct amount ofgas must be exchanged between a pair of beds in each such step, acrossthe continuously changing pressure difference between that pair of bedsduring the step, and over the time interval of that step.

Especially in large industrial PSA systems, it is also necessary toavoid high velocity transients that could damage the adsorbent byexcessive pressure gradients or fluidization. Such transients couldoccur as valve ports open at the beginning of an equalization orblowdown step. The internal geometry and orifice dimensions of amultiport distributor valve govern the amount of gas which can flowacross a given pressure gradient over a given time interval. Once theinternal orifice apertures of the rotary valves and piping connectionshave been fixed, the prior art PSA cycle using multiport valves couldonly operate correctly between given high and low pressures at one cyclefrequency with a given feed composition, and would have no means foroperational adjustment to optimize cycle performance.

Hence, prior art PSA devices with multiport valves would be unable tooperate at much reduced cycle frequency during periods of reduced demandfor purified product. It would be highly desirable to reduce cyclefrequency when product demand is reduced, since lower frequencyoperation would be more efficient at lower flows, less stressful on theadsorbent and valve components, and less noisy in medical applications.

The ability to adjust operating frequency is also vital for applicationswhere a product purity specification must be satisfied, while thehighest attainable product recovery is desired from a feed mixture ofgiven composition and flow rate and working between given higher andlower pressures. If the cycle frequency is too slow, the apparatus willrelease a relatively small exhaust flow at the lower pressure, resultingin high recovery of the light product at less than specified purity. Ifthe cycle frequency is moderately too high, the apparatus will release alarger exhaust flow, achieving higher than desired purity and lower thandesired recovery of the light product. If the cycle frequency is muchtoo high, mass transfer effects may degrade performance to result inunsatisfactory light product purity as well as low recovery. Suchapplications arise for example in industrial hydrogen purification. Inthese applications, cycle frequency must be adjustable in order toachieve specified purity and simultaneously high recovery of the lightproduct.

None of the cited prior art for pressure swing adsorption with multiportvalves addresses the combined need for adjustable cycle frequencycontrol and adjustable flow controls for gas exchanges between pairs ofadsorbent beds. There is no flow control other than the pressure dropresistance of the conduits and the valve ports as they open and close.Hence, these devices as disclosed have the operational limitation thatthey cannot be operated at significantly varied conditions of cyclefrequency and pressure.

It is well known that there is much scope for optimization of PSA cyclesby adjusting the pressure intervals taken up by different steps. Forexample, Suh and Wankat (AlChE Journal 35, pages 523-526, 1989) havepublished computer simulation results showing the sensitivity toadjustment between the pressure intervals allocated to cocurrent andcountercurrent blowdown. They showed that the optimum split between thepressure intervals for cocurrent and countercurrent blowdown issensitive to the feed gas composition and the adsorbent selectivity.Product recovery performance is degraded by operation away from theoptimum operating point.

The above cited PSA devices with multiport distributor valves lack anycontrol means for making adjustments between the pressure intervalstaken up by the different steps of the cycle. It would be very desirableto provide a control system capable of such adjustment while the PSAsystem is operating.

A further limitation of the prior art for PSA devices using multiportvalves is the lack of control means to establish relatively smooth andconstant flow over each step. Such control means could usefullyalleviate the flow inrush at the beginning of each step when valve portsopen across pressure differences, thus protecting the adsorbent bed andvalve ports from transient flow velocities much in excess of the averageflow during each step. Such control means could also minimize the timeintervals of zero or much below average flow velocity during valveswitching between steps, thus enhancing the productivity of theapparatus.

DISCLOSURE OF INVENTION

The pressure swing adsorption (PSA) process separates a feed gascontaining a first component which is more readily adsorbed, and asecond component which is less readily adsorbed, on an adsorbentmaterial installed in adsorbent beds. The PSA apparatus has a number “N”of adsorbent beds operating in parallel, and phased 360°/N apart inoperating sequence. Each adsorbent bed has a flow path through theadsorbent material, the flow path having a first end to which the morereadily adsorbed fraction of the feed gas mixture is separated by thePSA process, and a second end to which the less readily adsorbedfraction of the feed gas mixture is separated. Cocurrent flow in theflow path is directed from the first to the second end of the flow path,and countercurrent flow is directed from the second to the first end ofthe flow path.

Pressure swing adsorption processes, including that of the presentinvention, include some or all of the following sequential andcyclically repeated steps for each of the adsorbent beds:

-   -   (A) feed step at the higher pressure of the cycle,    -   (B) one or more equalization steps for initial depressurization        of the bed from the higher pressure to approach an equalization        pressure, while gas withdrawn to depressurize the bed is        supplied to another bed being pressurized in its step (F) toward        the same equalization pressure,    -   (C) cocurrent blowdown of the bed to an intermediate pressure        lower than the lowest equalization pressure but higher than the        lower pressure,    -   (D) countercurrent blowdown of the bed to approach the lower        pressure,    -   (E) purge step at substantially the lower pressure, with        countercurrent flow of gas from step (C),    -   (F) equalization step(s) repressurizing the bed to approach an        equalization pressure, with gas supplied to pressurize the bed        being withdrawn from another bed undergoing step (B),    -   (G) repressurization of the bed to approach the higher pressure.

The present invention achieves pressurization and depressurization stepsprimarily by gas exchanges between the adsorbent beds. Steps entailingexchange of gas enriched in the second component between adsorbent bedswill be described as light reflux steps. A predetermined logicalsequence of the process steps will be established by rotary distributorvalves, while flow regulation controls will enable satisfactoryoperation under varied process conditions and under varied cyclefrequencies so that required product purity, recovery and output can beachieved by a simple control strategy.

The following terminology and definitions will be used hereunder for PSAdevices using multiport distributor rotary valves. The first and secondends of the adsorbent beds are respectively connected in parallel tocontrol valves which in the present invention include multiportdistributor valves, a first distributor valve connected to the firstends of the adsorbent beds, and a second distributor valve connected tothe second ends of the beds.

Each rotary valve has two relatively rotating ported valve elements,respectively the valve stator and rotor. The relative rotation of thevalve elements sliding on a close contact sealing valve surface bringsthe ports of each element into sequential engagement. The valve surfaceis a surface of revolution, centered on the axis of revolution. Thevalve surface may be defined by flat discs, cones, circular cylinders,or other surface of revolution. The radial and axial position on thevalve surface of a cooperating set of ports on the two valve elementsmust substantially coincide.

The adsorbent beds are connected to adsorbent bed ports on one of thevalve elements, here described as the bed port element. Externalconnections for feed supply, product delivery and exhaust discharge aremade to function ports on the other valve element, here described as thefunction port element. Other function ports on the function port elementwill be provided for product reflux steps or for gas exchanges betweenpairs of adsorbent beds, e.g. for purge or pressure equalization steps.

The function ports have a critical role in defining the sequence andflow intervals for bed pressurization and blowdown steps. The presentinvention provides adjustable flow regulation controls, e.g. throttleorifices, on the conduits connecting pairs of function ports providedfor gas exchanges between adsorbent beds. These flow controls maycooperate directly with either the bed port element or the function portelement. In the example of pressure equalization steps, the flowcontrols must establish sufficient gas flow over the time interval ofthat pressure equalization step to achieve the desired pressure changesin the beds undergoing equalization, while avoiding excessively hightransient gas flows that may damage the adsorbent. Adjustability of theflow controls is required to achieve a satisfactory pressure and flowregime, particularly when changing the PSA cycle frequency, workingpressures, or feed gas composition or temperature.

The invention provides a process for separating first and secondcomponents of a feed gas mixture, the first component being more readilyadsorbed under increase of pressure relative to the second componentwhich is less readily adsorbed under increase of pressure over anadsorbent material, such that a gas mixture of the first and secondcomponents contacting the adsorbent material is relatively enriched inthe first component at a lower pressure and is relatively enriched inthe second component at a higher pressure when the pressure is cycledbetween the lower and higher pressures at a cyclic frequency of theprocess defining a cycle period; providing for the process a pluralityof adsorbent beds of the adsorbent material with a number “N” ofsubstantially similar adsorbent beds, with said adsorbent beds havingfirst and second ends; and further providing for the process a firstrotary distributor valve connected in parallel to the first ends of theadsorbent beds and a second rotary distributor valve connected inparallel to the second ends of the adsorbent beds, with flow controlscooperating with the first and second distributor valves; introducingthe feed gas mixture at substantially the higher pressure to the firstdistributor valve; and rotating the first and second distributor valvesso as to perform in each adsorbent bed the sequentially repeated stepswithin the cycle period of:

-   -   (A) supplying a flow of the feed gas mixture at the higher        pressure through the first distributor valve to the first end of        the adsorbent bed during a feed time interval, withdrawing gas        enriched in the second component (light reflux gas) from the        second end of the adsorbent bed, and delivering a portion of the        gas enriched in the second component as a light product gas,    -   (B) withdrawing a flow of gas enriched in the second component        (light reflux gas) from the second end of the adsorbent bed        through the second distributor valve, so as to depressurize the        adsorbent bed from the higher pressure toward an equalization        pressure less than the higher pressure, while controlling the        flow so that the pressure in the bed approaches the equalization        pressure within an equalization time interval, and also        controlling the flow so as to limit the peak flow velocity        exiting the second end of the adsorbent bed in that time        interval so as to avoid damaging the adsorbent,    -   (C) withdrawing a flow of gas enriched in the second component        (light reflux gas) from the second end of the adsorbent bed        through the second distributor valve, so as to depressurize the        adsorbent bed from approximately the equalization pressure to an        intermediate pressure less than the equalization pressure and        greater than the lower pressure, while controlling the flow so        that the pressure in the bed reaches approximately the        intermediate pressure within a cocurrent blowdown time interval,        and also controlling the flow so as to limit the peak flow        velocity exiting the second end of the adsorbent bed in that        time interval so as to avoid damaging the adsorbent,    -   (D) withdrawing a flow of gas enriched in the first component        (countercurrent blowdown gas) from the first end of the        adsorbent bed through the first distributor valve, so as to        depressurize the adsorbent bed from approximately the        intermediate pressure to approach the lower pressure, while        controlling the flow so that the pressure in the bed approaches        the lower pressure within a countercurrent blowdown time        interval, and also controlling the flow so as to limit the peak        flow velocity adjacent the first end of the adsorbent bed in        that time interval so as to avoid damaging the adsorbent,    -   (E) supplying a flow of gas enriched in the second component        (light reflux gas) from the second distributor valve to the        second end of the adsorbent bed at substantially the lower        pressure, while withdrawing gas enriched in the first component        from the first end of the adsorbent bed and through the first        distributor valve over a purge time interval, the flow of gas        enriched in the second component from the second distributor        valve being withdrawn from another of the adsorbent beds which        is undergoing cocurrent blowdown step (C) of the process,    -   (F) supplying a flow of gas enriched in the second component        (light reflux gas) from the second distributor valve to the bed,        so as to repressurize the adsorbent bed from approximately the        lower pressure to approach the equalization pressure, while        controlling the flow so that the pressure in the bed approaches        the equalization pressure within an equalization time interval,        and also controlling the flow so as to limit the peak flow        velocity entering the first end of the adsorbent bed in that        time interval so as to avoid damaging the adsorbent, the flow of        gas enriched in the second component from the second distributor        valve being withdrawn from another of the adsorbent beds which        is undergoing equalization step (B) of the process,    -   (G) supplying a flow of gas enriched in the second component        (light reflux gas) from the second distributor valve to the bed,        so as to repressurize the adsorbent bed from the equalization        pressure to approach the higher pressure, while controlling the        flow so that the pressure in the bed approaches the higher        pressure within a repressurization time interval, and also        controlling the flow so as to limit the peak flow velocity        entering the second end of the adsorbent bed in that time        interval so as to avoid damaging the adsorbent, the flow of gas        enriched in the second component from the second distributor        valve being withdrawn from another of the adsorbent beds which        is undergoing feed step (A) of the process,    -   (H) cyclically repeating steps (A) to (G).

Steps (A) to (F) inclusive are conducted successively in the “N”adsorbent beds, in different phases separated by a fraction “1/N” of thecycle period.

The invention provides an apparatus for separating the first and secondcomponents of the feed gas mixture, with:

-   -   (a) a number “N” of substantially similar adsorbent beds of the        adsorbent material, with said adsorbent beds having first and        second ends defining a flow path through the adsorbent material;    -   (b) light product delivery means to deliver a light product flow        of gas enriched in the second component from the second ends of        the adsorbent beds;    -   (c) a first rotary distributor valve connected in parallel to        the first ends of the adsorbent beds; the first distributor        valve having a stator and a rotor rotatable about an axis; the        stator and rotor comprising a pair of relatively rotating valve        elements, the valve elements being engaged in fluid sealing        sliding contact in a valve surface, the valve surface being a        surface of revolution coaxial to the axis, each of the valve        elements having a plurality of ports to the valve surface and in        sequential sliding registration with the ports in the valve        surface of the other valve element through the relative rotation        of the valve elements; one of said valve elements being a first        bed port element having N first bed ports each communicating to        the first end of one of the N adsorbent beds; and the other        valve element being a first function port element having a        plurality of first function ports including a feed port, a        countercurrent blowdown port and a purge exhaust port; with the        bed ports spaced apart by equal angular separation between        adjacent ports; and with the first function ports and first bed        ports at the same radial and axial position on the valve surface        so that each first function port is opened in sequence to each        of the N first bed ports by relative rotation of the valve        elements;    -   (d) a second rotary distributor valve connected in parallel to        the second ends of the adsorbent beds and cooperating with the        first distributor valve; the second distributor valve having a        stator and a rotor rotatable about an axis; the stator and rotor        comprising a pair of relatively rotating valve elements, the        valve elements being engaged in fluid sealing sliding contact in        a valve surface, the valve surface being a surface of revolution        coaxial to the axis, each of the valve elements having a        plurality of ports to the valve surface and in sequential        sliding registration with the ports in the valve surface of the        other valve element through the relative rotation of the valve        elements; one of said valve elements being a second bed port        element having N second bed ports each communicating to the        second end of one of the N adsorbent beds; and the other valve        element being a second function port element having a plurality        of second function ports including a plurality of light reflux        withdrawal ports and light reflux return ports, with each light        reflux return port communicating through the second function        element to a light reflux withdrawal port; with the bed ports        spaced apart by equal angular separation between adjacent ports;        and with the function ports and bed ports at the same radial and        axial position on the valve surface so that each function port        is opened in sequence to each of the N bed ports by relative        rotation of the valve elements;    -   (e) drive means to establish rotation of the rotors, and hence        relative rotation of the bed port elements and the function port        elements, of the first and second distributor valves, with a        phase relation between the rotation of the rotors and angular        spacing of the function ports of the first and second        distributor valves so as to establish for each adsorbent bed        communicating to corresponding first and second bed ports the        following sequential steps and cyclically repeated steps for        those bed ports;        -   (i) the first bed port is open to the feed port, while light            product gas is delivered by a light product delivery valve,        -   (ii) the second bed port is open to a light reflux            withdrawal port,        -   (iii) the first bed port is open to the countercurrent            blowdown port,        -   (iv) the first bed port is open to the purge exhaust port,            while the second bed port is open to a light reflux return            port;    -   (f) countercurrent blowdown flow control means cooperating with        the first distributor valve; (g) light reflux flow control means        cooperating with the second distributor valve; (h) feed supply        means to introduce the feed gas mixture to the feed port of the        first distributor valve at substantially the higher pressure;        and    -   (i) exhaust means to remove gas enriched in the first component        from the purge exhaust port of the first distributor valve.

The flow control means cooperating with the first and second distributorvalves (for respectively countercurrent blowdown and light reflux steps)may be provided as continuously adjustable orifices (e.g. throttlevalves), or as discretely adjustable orifices with selector valves toswitch between discrete settings. The light reflux flow control meansmay be provided as adjustable orifices within the rotor of the seconddistributor valve, or as adjustable orifices interposed between thesecond end of each of the adsorbent beds and the second distributorvalve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified schematic of a six bed PSA apparatus with onepressure equalization step.

FIG. 2 shows the valve port geometry for the first distributor valve ofthe apparatus of FIG. 1.

FIG. 3 shows the valve port geometry for the second distributor valve ofthe apparatus of FIG. 1.

FIG. 4 shows the valve timing and pressure waveform for the apparatus ofFIG. 1 with valve port geometry of FIGS. 2 and 3.

FIGS. 5 and 6 show modified valve timing and pressure waveforms for theapparatus of FIG. 1.

FIG. 7 shows idealized pressure transients for the apparatus with asingle pressure equalization step.

FIG. 8 shows an alternative schematic of a six bed PSA apparatus withprovision for two equalization steps.

FIG. 9 shows valve timing and the pressure waveform for the apparatus ofFIG. 8.

FIG. 10 shows mechanical actuators for the adjustable orifices.

FIG. 11 shows a second distributor valve with fluid transfer chambersthrough the stator housing to the adjustable orifices.

FIG. 12 shows an oscillating angular velocity mechanical drive for thefirst distributor valve.

FIG. 13 shows a pressure-balanced embodiment of the first distributorvalve.

FIG. 14 is an axial section of the valve of FIG. 13.

FIG. 15 is a longitudinal section of another pressure-balancedembodiment of the first distributor valve.

FIG. 16 shows an adjustable orifice with two discrete settings,applicable to the apparatus of FIG. 1.

It is noted that FIGS. 1, 8, 10, 11 and 13 are schematic diagrams ofembodiments of the invention, showing rotary distributor valves inlongitudinal section along their axis of rotation. In order toillustrate the interconnections of the apparatus, all of the bed portsand function ports of the depicted distributor valves are shown in thesesimplified schematics; with the ports therefore shown in arbitrarypositions not representing the actual geometric arrangement of the portsas provided for example in the axial sections of FIGS. 2 and 3.Geometrically true longitudinal sections of these valves (such as FIG.15) would show at most pairs of bed ports and function ports at a singleradial distance on opposite sides of the axis of rotation.

MODES FOR CARRYING OUT THE INVENTION

FIG. 1

A pressure swing adsorption apparatus 1 is operated in a pressure swingadsorption cycle at an cyclic frequency characterized by a period “T”.The apparatus has a number “N”=6 of substantially similar adsorbent beds2, 3, 4, 5, 6 and 7. The beds have first ends 8, 9, 10, 11, 12 and 13;and second ends 14, 15, 16, 17, 18 and 19. The adsorbent material ineach bed defines a flow path between first and second ends of that bed.

The first end of each adsorbent bed communicates by bed conduits 20, 21,22, 23, 24 and 25 to corresponding first bed ports 30, 31, 32, 33, 34and 35 in stator 36 of first rotary distributor valve 37. The stator isattached within stator housing 38, by sealing means such as adhesivebonding so that no pathway is provided between the stator and statorhousing for gas leakage between the bed conduits.

The first distributor valve includes a rotor 40, driven by first valvedrive means 41 through shaft 42 about axis of rotation 43. The rotor 40and stator 36 are engaged in mutual fluid sealing sliding contact onvalve surface 45, which is a surface of revolution about axis 43. Thebed ports 30-35 open to valve surface 45. The rotor has a plurality offirst function ports also open to the valve surface, including a feedport 50, a countercurrent blowdown port 51 and a purge exhaust port 52.

The rotor and stator are the relatively rotating valve elements of thedistributor valve. The stator may be described as the first bed portelement of the valve, while the rotor is the first function port elementof the valve.

The second end of each adsorbent bed communicates by one of conduits 55,56, 57, 58, 59 and 60 through light reflux flow controls (e.g.adjustable orifices) 61, 62, 63, 64, 65 and 66 respectively tocorresponding second bed ports 70, 71, 72, 73, 74 and 75 in stator 76 ofsecond rotary distributor valve 77. The stator is attached within statorhousing 78 so that no pathway is provided between the stator and statorhousing for gas leakage between the bed conduits. The rotor and statorare the relatively rotating valve elements of the distributor valve. Thestator may be described as the second bed port element of the valve,while the rotor is the second function port element of the valve.

The second distributor valve includes a rotor 80, driven by second valvedrive means 81 through shaft 82 about axis of rotation 83. The rotor 80and stator 76 are engaged in mutual fluid sealing sliding contact onvalve surface 85, which is a surface of revolution about axis 83. Thebed ports 70-75 open to valve surface 85. The rotor has a plurality ofsecond function ports also open to the valve surface.

The second function ports are provided as pairs of light refluxwithdrawal and light reflux return ports, with each light refluxwithdrawal port communicating to a light reflux return port through anadjustable orifice in rotor 80. Light reflux withdrawal port 90communicates through adjustable orifice 96 in the rotor to light refluxreturn port 93. Light reflux withdrawal port 91 communicates throughadjustable orifice 97 in the rotor to light reflux return port 94. Lightreflux withdrawal port 92 communicates through adjustable orifice 98 inthe rotor to light reflux return port 95.

As FIG. 1 is a schematic diagram of the apparatus, all of the bed portsand function ports of the first and second distributor valves are shownon the valve surfaces in FIG. 1 so that all connections to the ports maybe shown. Hence, FIG. 1 does not indicate the actual geometricarrangement and timing sequence of the ports which are shown in FIGS. 2and 3. As will be evident from FIGS. 2 and 3, the bed and function portsin each distributor valve will be located at a fixed radius from theaxis of rotation.

While valve surfaces 45 and 85 are depicted as flat discs, they could becones, cylinders, or other surface of revolution. While flat disc valvesare preferred for smaller units because leakage is readily minimized,cylindrical barrel valves may be preferred for much larger units inorder to avoid excessively large valve rotor diameter and friction. Therespective materials for the mating surfaces of the stator and rotor insliding contact on the valve surface may include ceramic or hardenedmetal alloy for one valve element, and carbon or a self-lubricatingpolymeric compound (for example based on PTFE) for the other element, soas to minimize friction and wear.

The first and second distributor valves are provided with loading meansto ensure sealing contact of the rotor and stator on the valve surface.Such loading means may include mechanical springs 100 and 101,respectively loading rotors 40 and 80 by thrust washers 102 and 103.

The loading means may also include gas pressure loading, applied eitherexternally or else internally as here depicted. In the seconddistributor valve 77, rotary seals 105 and 106 between rotor 80 andstator housing 78 are provided with different diameters, definingannular chamber 107 in the housing. Chamber 107 communicates in rotor 80with light reflux withdrawal port 90, and in stator housing 78 withsurge chamber 108. Chamber 109 in the housing is defined externally ofrotary seal 106, and communicates in rotor 80 with light reflux returnport 95 and in stator housing 78 with surge chamber 110.

In the first distributor valve 37, rotary seals 112 and 113 betweenrotor 40 and stator housing 38 define an outer sealing diameter. Therotor and housing are stepped down to a smaller sealing diameter forrotary seals 114 and 115, in turn larger in diameter than rotary shaftseal 116. The diameter difference between rotary seals 113 and 114defines annular chamber 120 between the rotor and housing. Chamber 120communicates in rotor 40 with purge exhaust port 52, and in statorhousing 38 with purge exhaust conduit 121. The diameter differencebetween rotary seals 115 and 116 defines annular chamber 125 between therotor and housing. Chamber 125 communicates in rotor 40 with feed port50, and in stator housing 38 with feed supply conduit 126 throughtransfer chamber 127 defined by rotary seals 114 and 115.

Seals 112 and 113 between rotor 40 and housing 38 define annulartransfer chamber 130, communicating in the rotor to countercurrentblowdown port 51 and in the housing by countercurrent blowdown conduit131 to countercurrent blowdown flow control valve 132, communicatingwith purge exhaust conduit 121 to exhaust conduit 133.

Optionally, a heavy reflux portion of the gas enriched in the firstcomponent from preferably the purge exhaust conduit may be recompressedby heavy reflux compressor 135 to the feed supply conduit 126. Athree-way feed selector valve 136 is provided to accept gasalternatingly from heavy reflux compressor 135 via conduit 137 and fromfeed conduit 138, and to deliver this gas to feed supply conduit 126.Feed gas mixture enters the apparatus by infeed conduit 139 to feedcompressor 140, and thence by conduit 138 to feed selector valve 136.Surge chambers between the selector valve 136, and compressors 135 and140, may be needed to absorb flow pulsations as the selector valve isactuated.

An alternative configuration is to install a combined feed compressor141 (shown in dashed outline) in feed supply conduit 126, downstream offeed selector valve 136. The combined feed compressor compresses thecombination of feed and heavy reflux gases, received as a substantiallysteady gas flow from feed selector valve 136, alternatingly feed gasreceived from conduit 138 and heavy reflux gas received from conduit137. If the exhaust pressure in conduit 133 is less than the feedpressure in conduit 139, feed compressor 140 may be eliminated whileheavy reflux compressor 135 would be retained. If the exhaust pressurein conduit 133 is substantially equal to the feed pressure in conduit139, feed compressor 140 and heavy reflux compressor 135 may both beeliminated, so that combined feed compressor 141 performs the combinedduties of feed and heavy reflux compression.

The purpose of heavy reflux is to increase recovery of the secondcomponent in the light product, or equivalently to increaseconcentration of the first component in the heavy product dischargedfrom exhaust conduit 133. In the option that heavy reflux is not used,compressor 135 and selector valve 136 would be eliminated so that feedgas from compressor 140 enters feed supply conduit 126 directly.

Infeed conduit 139 and feed compressor 140 (or alternative feedcompressor 141) are feed supply means to the apparatus. If the feedcompressor was omitted, the feed gas would be supplied by an externalsource to infeed conduit 139 at approximately the higher workingpressure of the process.

It will be evident that transfer chambers 127, 130 and 120 serverespectively to transfer gas from the first function ports 50, 51 and 52to corresponding function conduits in the first valve stator housing.

A product delivery check valve is provided for each adsorbent bed,communicating from the second end of that bed to a light productmanifold. Product gas enriched in the second component is withdrawn fromthe second ends of the adsorbent beds by light product delivery valvemeans, here provided as product delivery check valves 144, 145, 146,147, 148 and 149 delivery light product gas from beds 2, 3, 4, 5, 6 and7 to light product manifold 150 and light product pressure and/or flowregulation means 151. It may be noted that the light product gas and thelight reflux gas may not be identical in composition, as the lightproduct gas will preferably be more highly enriched or purified in thesecond component.

The rotary distributor valve drive means 41 and 81 are synchronized.Thus, drive means 41 and 81 may be gear reducers, driven bysynchronizing drive linkages 152 and 153, which in turn may be driven bya variable speed drive 154 and motor 155. Drive linkages 152 and 153 mayuse line shafts or chain drives. Actuation means 160 for feed selectorvalve 136 may cooperate with first valve drive means 41 throughsynchronizing timing control 161. Control 161 and actuator 162 may beprovided as a cam drive on shaft 42, cycling selector valve 136 fromfeed to heavy reflux back to feed six times per revolution of shaft 42.

Control means for the apparatus include a cycle frequency controller 162controlling the variable speed drive 154, actuator 163 and valve 132countercurrent blowdown flow control valve 132, and a light reflux flowcontrol which may be light reflux flow control valves 61-66 whoseactuation is coordinated by controller 164. A supplementary oralternative light reflux flow control may be provided by adjustableorifices 96-98 in the second distributor valve. Cycle frequency mayalternatively be controlled by variable frequency AC or by variablevoltage DC control of motor 155, or by any other means to adjust rotaryshaft speed.

This apparatus enables the process of the invention to vary cyclefrequency, so as to achieve desired purity, recovery and flow rate ofthe light product gas. Higher flow rates, both of feed and of lightproduct gas, may in general be achieved by operating the apparatus athigher cycle frequency, expressed as valve RPM. Apart from ultimatemechanical limits to higher cycle frequency that may result fromconsiderations of adsorbent bed attrition or rotary valve frictionalheating, the highest useful cycle frequency will be determined by masstransfer degradation of adsorbent bed performance, typically controlledby macropore diffusion. Gas separation performance (e.g. ability toachieve target purity and recovery of light product) will be degraded athigher frequencies by mass transfer effects impeding equilibrationbetween the adsorbate and interstitial gas.

When the process is operating in a range of cycle frequencies in whichgas separation performance is not greatly degraded by mass transfereffects, the process (operating between given higher and lowerpressures) will operate as an escapement to release exhaust gas enrichedin the heavy component. When the feed flow (as well as the higher andlower pressures) is held constant, recovery of the light product willthen be enhanced by reducing cycle frequency, while light product puritywill be degraded if cycle frequency is reduced too much. Conversely,under these conditions of fixed feed flow rate and working pressurerange, light product purity will be enhanced at the expense of lightproduct recovery by increasing cycle frequency, before reaching suchhigh cycle frequencies that purity would be degraded by mass transferlimitations. If target purity and recovery cannot be achieved with agiven feed flow rate by adjusting cycle frequency, the feed flow rateshould be reduced. Owing to mass transfer influences, highest lightproduct purity and recovery will be achievable at lower cyclefrequencies and with lower feed flows, resulting in relatively low lightproduct flow rates.

FIGS. 2 and 3

FIG. 2 shows the arrangement of the bed ports on the stator 36 and ofthe function ports on the rotor 40, in the plane of the valve surface45. The first bed ports 30-35 and the first function ports 50-52 arelocated on the valve surface at the same axial and radial position, sothat each first function port is opened in sequence to each of the firstbed ports as the valve rotates. The bed ports are spaced apart by equalangular separation between adjacent ports, here 60° for six beds.

As shown in FIG. 3, the second bed ports 70-75 on stator 76 and thesecond function ports 90-95 on rotor 80 are located on the valve surface85 at the same axial and radial position, so that each second functionport is opened in sequence to each of the second bed ports as the valverotates. The bed ports are spaced apart by equal angular separationbetween adjacent ports.

The rotors as shown in FIGS. 2 and 3 rotate clockwise over the stators,as indicated by arrows 168 and 169. The rotors are depicted at the sameinstant of time, or equivalently at the same angular position relativeto the bed ports, in FIGS. 2 and 3.

It will be noted that feed port 50 has an overlapping angular positionwith light reflux withdrawal port 90, while purge exhaust port 52 has anoverlapping angular position with light reflux return port 95.

Alternatively, port 50 could be opened earlier than port 90, as shown bybroken outline 170 advancing the leading edge of port 50. Earlieropening of port 50 would provide for feed pressurization of an adsorbentbed, in the final interval before port 90 opens. Feed pressurization, inthe final stage of pressurization approaching the higher pressure of thecycle, and cooperating with or instead of product pressurization, isrecognized in the art as a desirable alternative to pressurization byproduct alone.

Apparatus 1 operates in a pressure swing adsorption cycle between ahigher pressure, here established by feed compressor 140, and a lowerpressure established by the exhaust pressure in exhaust conduit 133. Inoperation of the apparatus 1, the raw feed gas mixture is supplied atsubstantially the higher pressure to feed port 50, while gas enriched inthe first component is withdrawn by conduit 121 and transfer chamber 120from purge exhaust port 52 at substantially the lower pressure.

Hence annular chamber 125 is pressurized at approximately the higherpressure, and annular chamber 120 is pressurized at approximately thelower pressure, establishing the gas pressure loading of the rotor 40 onstator 36 according to the relative diameters of seals 113, 115 and 116defining the axially projected annular areas of chambers 120 and 125.

With a desirable low pressure drop due to flow in the adsorbent beds,light reflux withdrawal port 90 which is angularly aligned with feedport 50 will be pressurized to approximately the higher pressure by gasflow through the beds to which ports 50 and 90 are simultaneously open.Similarly, light reflux return port 95 which is angularly aligned withpurge exhaust port 52 will be pressurized to approximately the lowerpressure by gas flow through the beds to which ports 52 and 95 aresimultaneously open.

Hence annular chamber 107 is pressurized at approximately the higherpressure, and annular chamber 109 is pressurized at approximately thelower pressure, establishing the gas pressure loading of the rotor 80 onstator 76 according to the relative diameters of seals 105 and 106 andthe diameter of the rotor 80 on the valve surface. These diametersdefine the axially projected annular areas of chambers 107 and 109.

The process of the invention may be understood by considering FIGS. 2and 3 together with FIG. 4.

FIG. 4

Corresponding to the function port geometry of FIGS. 2 and 3, FIG. 4shows valve timing diagram 200 for the second distributor valve, valvetiming diagram 201 for the first distributor valve, and the pressurewaveform for typical adsorbent bed 2 communicating to second bed port 70and first bed port 30.

The angular positions of the ports of the distributor valves are shownin diagram 200 for the second function ports in row 205 and the secondbed ports in row 206, and in diagram 201 for the first function ports inrow 207 and the first bed ports in row 208. The rotation of the valvescauses the rows of function ports 205 and 207 to move leftward indiagrams 200 and 201, for a total movement of 360° in each cycle periodT, as shown by arrows 210 and 211.

At the instant of time depicted in FIG. 4, bed 2 has just completed afeed step, in which a flow of the feed gas mixture was supplied at thehigher pressure P_(H) through feed port 50 open to bed port 30 and thefirst end 8 of the bed 2 during a feed time interval (300° to 360°),while gas enriched in the second component was withdrawn from the secondend 14 of the bed. A portion of the gas enriched in the second componentwas delivered in the feed step as a light product gas by productdelivery check valve 144, while the remainder of the gas enriched in thesecond component was withdrawn as light reflux gas for repressurizationthrough light reflux flow control valve 61, as bed port 70 was open tolight reflux withdrawal port 90.

During the feed step, the pressure is maintained at substantially thehigher pressure P_(H). Flow control in the feed may be established bythe sum of the feed flow and any heavy reflux flow admitted to transferchamber 127 and feed port 50 of the first distributor valve, with thelight product flow being the excess by mass balance over the exhaustflow enriched in the first component removed from exhaust conduit 133.Heavy reflux flow reduces the quantity of exhaust gas discharged fromexhaust conduit 133, increasing concentration of the first component inthe exhaust flow and improving recovery of the second component in thelight product gas.

Alternatively, the feed supply means may establish the feed pressure atsubstantially the higher pressure, without directly controlling flow ofthe feed gas, e.g. in the case that feed compressor 140 is omitted. Theflow control during the feed step may then be established by controllingthe light product flow, e.g. by the volumetric capacity of light productcompressor 151. Usually, the higher pressure P_(H) of the cycle will becontrolled by downstream light product pressure regulation by regulator151.

If heavy reflux compressor 135 and selector valve 136 are included, aportion of the purge exhaust flow and/or the countercurrent blowdownflow is recompressed as an internally recycled second feed to theapparatus. The heavy reflux gas or second feed is enriched in the firstcomponent compared to the feed gas mixture. In order to maintain adesired concentration gradient in the adsorbent bed, with higherconcentration of the first component at the first end of the bed andhigher concentration of the second component at the second end of thebed, the heavy reflux or second feed (enriched in the second componentrelative to the feed) should be admitted later in the feed step, afterthe feed gas has been admitted earlier in the feed step. Hence selectorvalve 136 would admit the feed gas mixture from feed compressor 140 tofeed supply conduit 126 in the first part of the feed step (e.g. 300° to330°) for bed 2, and would then admit the heavy reflux (or second feed)from heavy reflux compressor 135 to feed supply conduit 126 in thesecond part of the feed step (e.g. 330° to 360°) for bed 2. The processaspect here is providing a feed selector valve to alternatingly directthe feed gas mixture or the heavy reflux gas through the firstdistributor valve to the first end of the adsorbent bed, and switchingthe feed selector valve at a frequency “N” times the cycle frequency foran apparatus of “N” adsorbent beds in parallel.

The above principle of switching in the feed step from a feed gasmixture to a second feed gas of greater concentration in the firstcomponent may be generalized in the present invention. Thus, the secondfeed gas may be provided externally as a gas mixture leaner in a desiredsecond component than the first feed gas hitherto referred to as thefeed gas mixture. More than two feed gas mixtures, optionally includinga heavy reflux recompressed from the exhaust gas enriched in the firstcomponent, may be fed sequentially (in order of ascending concentrationin the first component) to the apparatus either through additional feedports in the first distributor valve or through additional selectorvalve channels to the feed port.

At the instant depicted in FIG. 4, bed 7 is beginning its feed step andbed 2 is just beginning an equalization depressurization step, in whichthe first valve is closed to bed 2, while a flow of gas enriched in thesecond component is withdrawn as light reflux gas from second end 14through light reflux flow control valve 61, as bed port 70 opens tolight reflux withdrawal port 91. This flow depressurizes the adsorbentbed from the higher pressure P_(H) toward an equalization pressureP_(EQ) less than the higher pressure, while the flow is controlled sothat the pressure in the bed approaches the equalization pressure withinan equalization time interval (0° to 30°) until port 91 closes to port70.

There is then a waiting time interval (30° to 60°) until light functionport 92 opens to bed port 70, beginning a cocurrent blowdown step. Aflow of light reflux gas enriched in the second component is withdrawnfrom second end 14 through light reflux flow control valve 61, as bedport 70 opens to light reflux withdrawal port 92. This flowdepressurizes the adsorbent bed from equalization pressure P_(EQ) to anintermediate pressure P_(INT) greater than the lower pressure P_(L),while the flow is controlled so that the pressure in the bed approachesintermediate pressure P_(INT) within a cocurrent blowdown time interval(60° to 120°) until port 92 closes to port 70.

The next step is countercurrent blowdown. A flow of gas enriched in thefirst component is withdrawn from the first end 8 of bed 2 throughtransfer chamber 130 and countercurrent blowdown flow control valve 132,as first bed port 30 opens to countercurrent blowdown port 51. This flowdepressurizes the adsorbent bed from intermediate pressure P_(INT) tothe lower pressure P_(L) while the flow is controlled so that thepressure in the bed approaches lower pressure P_(L) within acountercurrent blowdown time interval (120° to 180°) until port 51closes to port 30.

The next step is the purge step, conducted at lower pressure P_(L) overa purge time interval (180° to 240°). Purge exhaust port 52 opens tofirst bed port 30, while light reflux return port 95 opens to second bedport 70. A flow of gas enriched in the first component is withdrawn fromthe first end 8 of bed 2 through ports 30 and 52 to transfer chamber 120and exhaust conduit 133, while a light reflux flow of gas is returned tosecond bed port 70 from light reflux return port 95. This light refluxgas has been throttled from light reflux withdrawal port 92 byadjustable orifice 98, and was received from bed 6 undergoing thecocurrent blowdown step, as indicated by arrow 212. Port 74 of bed 6 isopen to light reflux withdrawal port 92 while port 70 of bed 2 is opento light reflux return port 95, communicating through orifice 98. Flowcontrol of light reflux gas exchange between beds 6 and 2 in this stepis established by orifice 98 in series with flow control valves 61 and65.

The next step is the equalization pressurization step, in which the bed2 is partially repressurized with gas exchanged from another bed 4undergoing partial depressurization from a higher pressure, over anequalization time interval (240° to 270°) for bed 2. Light reflux returnport 94 opens to second bed port 70 to admit a flow of light reflux gasto repressurize bed 2 from lower pressure P_(L) to approach theequalization pressure P_(EQ). This light reflux gas has been throttledfrom light reflux withdrawal port 91 by adjustable orifice 97, and wasreceived from bed 4 undergoing the equalization depressurization step,as indicated by arrow 213. Port 72 of bed 4 is open to light refluxwithdrawal port 91 while port 70 of bed 2 is open to light reflux returnport 94, communicating through orifice 97. Flow control of light refluxgas exchange between beds 4 and 2 in this step is established by orifice97 in series with flow control valves 61 and 63.

The following step is the pressurization step in which bed 2 isrepressurized back to the higher pressure over a repressurization timeinterval (270° to 300°). Light reflux return port 93 opens to second bedport 70 to admit a flow of light reflux gas to repressurize bed 2 fromequalization pressure P_(EQ) to approach the higher pressure P_(H). Thislight reflux gas has been throttled from light reflux withdrawal port 90by adjustable orifice 96 and was received from bed 3 undergoing the feedstep, as indicated by arrow 214. Port 71 of bed 3 is open to lightreflux withdrawal port 90 while port 70 of bed 2 is open to light refluxreturn port 93, communicating through orifice 96. Flow control of lightreflux gas exchange between beds 3 and 2 in this step is established byorifice 96 in series with flow control valves 61 and 62.

Pressurization to the higher pressure may alternatively be achieved atleast in part by earlier opening of feed port 50 (as shown by brokenoutline 170 advancing the leading edge of port 50) to a bed port 30 inthe first distributor valve while bed port 70 of the same adsorbent bed2 remains closed to light reflux withdrawal port 90 during therepressurization step. The working pressure in bed 2 will then riseuntil it reaches a pressure established by light product regulationmeans 151, at which point check valve 144 will open to deliver product.

In each step above, it is necessary to control the flow so as to avoidtransient peak flow velocities in the adsorbent bed that would damagethe adsorbent by excessively large transient pressure gradients, thuscontrolling the flow so as to limit the ratio of the peak flow velocityto the average flow velocity exiting the second end of the adsorbent bedin that time interval so as to avoid damaging the adsorbent.

An advantage to the distributor valve timing described in FIGS. 2, 3 and4 is that the light reflux exchanged between pairs of the six beds isalways exchanged directly through an adjustable orifice communicating inthe rotor between a light reflux withdrawal port open to one bed and alight reflux return port simultaneously open to another bed. This valvetiming has the disadvantage of a waiting period of 60° between theequalization depressurization step and the cocurrent blowdown step.Duration expressed as angular rotation of the light reflux steps in thediagram of FIG. 4 are 30° for equalization (depressurization andrepressurization), 60° for cocurrent blowdown and purge, and 30° forrepressurization. The unequal duration of these steps requires unequalsetting of the adjustable orifices 97 and 98 relative to orifice 96, aswill be explained in the discussion below of FIG. 7.

FIG. 5

FIG. 5 illustrates a modified timing diagram applicable to apparatus 1,in which the waiting period is eliminated in modified pressure waveform223. This is achieved by spacing the function ports as shown in FIG. 5.The cocurrent blowdown step is shifted to the interval 30° to 60°, andthus contracted to an angular duration of 30°, equal to the duration ofthe equalization step and the repressurization step. The countercurrentblowdown interval now spans the interval from 60° to 120°, while anextended purge step spans the interval from 120° to 240°. Since thispurge step is longer than needed, the cycle is improved by terminatingthe countercurrent blowdown at 120° before the pressure has dropped toP_(L), and then completing the depressurization in the early part of thepurge exhaust interval. This is achieved by shaping purge exhaust port52 to have a tapered leading edge 224 which opens to first bed port 30before light reflux return port 95 opens to second bed port 70 of bed 2.Also, countercurrent blowdown flow control valve 132 would be partiallyclosed to restrict the countercurrent blowdown flow so thatdepressurization is incomplete in the countercurrent blowdown step.

The extended countercurrent blowdown and purge steps enable someimprovement of cycle performance. However, the open interval of 30° forlight reflux withdrawal port 92 is no longer identical to the openinterval of approximately 60° for corresponding light reflux return port95. Hence, surge chamber 110 must be considerably enlarged to acceptcocurrent blowdown gas from port 92 after throttling through orifice 98,and then deliver that gas at substantially the lower pressure to lightreflux port 95 for the purge step, without excessive pulsations of flowor pressure.

FIG. 6

FIG. 6 illustrates a six bed cycle similar to that of FIG. 5, with adouble feed step rather than a double exhaust step. A second feed port226 provides for admission of a second feed in a second feed step, whichmay be heavy reflux or another gas enriched in the first componentrelative to the first feed gas mixture which is admitted in the firstfeed step.

If a single feed gas only is admitted to the apparatus, and there is noheavy reflux, the second feed port 226 may be extended to merge withfeed port 90, as indicated by dashed lines in FIG. 6. In that event, theadvantage of having a feed step of double length is to reduce flowvelocities during the feed step, so that upward gas flow velocities inthe adsorbent bed are minimized during the feed step, so as to avoid anyapproach to bed fluidization that would cause adsorbent attrition. Sinceupward flow velocities are reduced, the cycle of FIG. 6 may be operatedat higher cycle frequency while avoiding risks of bed attrition.

It will be evident that the cycles of FIGS. 5 and 6 could be modified byusing only five beds, with a single feed step and a single exhaust step.Conversely, cycles with more than six beds could be used to enableextended feed and/or exhaust steps, or to introduce additionalequalization steps.

The cyles of FIGS. 5 and 6 have the advantage that all light refluxsteps have the same duration, which simplifies control as will next beshown.

FIG. 7

Control of the process is now discussed. It is highly desirable that theprocess be capable of adjusting to changes of feed pressure, feedcomposition, and product demand. A preferred application of theinvention is recovery of hydrogen from refinery waste gases, where widevariations of feed pressure and composition, and of demand for purifiedproduct, may be normally expected.

Where feed composition is constant, as in the application of oxygenseparation from air, a capability for efficient turndown duringintervals of reduced product demand will often be required. The mostefficient turndown will be achieved by operating the process at reducedcycle frequency and reduced feed flow during intervals of reducedproduct delivery, so that power consumption can be reduced, whileoperating stresses and wear of valve components and the adsorbent arealso reduced.

While the distributor valves establish the timing logic and sequence ofthe cycle steps, the invention also provides flow controls for the stepsof the process.

These flow controls establish the correct pressure response of theadsorbent beds during depressurization and repressurization steps. It isparticularly important that light reflux steps be correctly controlled.

FIG. 7 shows calculated pressure transients through the seconddistributor valve for the equalization, cocurrent blowdown andrepressurization steps (the “light reflux” steps) of the process with asingle equalization step. The transients are plotted as pressure in anadsorbent bed undergoing each step, versus a time function “(A.t)/V”plotted on ordinate 250 from the beginning of that step. In the timefunction, “A” is the flow area of an orifice (one of orifices 96, 97, or98) in the second distributor valve rotor through which flow isoccurring to achieve that step, “t” is the time from the beginning ofthat step when the function ports communicating to that orifice open tothe bed ports of the beds undergoing that step, and “V” is the volume ofthat bed. Flow control of any of these light reflux steps may beobtained by adjusting the area “A” of the corresponding orifice.

The pressure transients were calculated on the basis of the followingassumptions. The light reflux gas is a pure second component which is adiatomic gas such as hydrogen, only weakly adsorbed with a linearisotherm and negligible heat of adsorption so the second end of theadsorbent bed remains isothermal. Flow controls 61-66 are assumed to bewide open, corresponding to the process condition of operation atmaximum cycle frequency. Pressure drops in the flow path within beds 2-7are neglected. Pressure drop associated with incomplete opening of theports in second valve surface 85 is also neglected, equivalent to theassumption (approximately valid for small units with small diameter bedports) that these ports are opened instantaneously at the beginning ofeach of the steps considered. The pressure drop associated with gasexchange flows between adsorbent beds was calculated on the basis ofadiabatic compressible flow of a diatomic gas, for the case of the PSAcycle pressure ratio P_(H):P_(L) assumed as 4:1.

Curve 260 shows equalization depressurization of a bed, exchanging gasas indicated by arrow 261 through orifice 97 to another bed whoseequilization pressurization response is shown by curve 262. Curve 263shows cocurrent blowdown of a bed releasing gas as shown by arrow 264 toa bed undergoing the purge step. Curve 265 shows displacement of thecocurrent blowdown, by starting from a pressure 266 somewhat higher thanPEQ as the result of terminating the equalization depressurization stepat a value of the time coefficient 267. Curve 268 shows therepressurization step of a bed, receiving light reflux gas as indicatedby arrow 269 from a bed undergoing the feed step.

In the case that the cocurrent blowdown for a bed is also terminated ata time corresponding to value 267 of the time coefficient (with assumedinstantaneous closing of the valve ports in the valve surface 85), thepressure in that bed has dropped to P_(IN).

For the example of oxygen separation from air over zeolitespreferentially adsorbing nitrogen as the second component, computermodelling and experimental testing of the six bed PSA cycle defined byFIG. 4 has shown that an optimum amount of countercurrent blowdown isestablished when the intermediate pressure is in the range definedapproximately by(P_(INT)−P_(L))/(P_(H)−P_(L))=0.20 to 0.25.This optimal ratio would take lower values of(P_(INT)−P_(L))/(P_(H)−P_(L))=0.15 to 0.20when the first component is more strongly adsorbed than nitrogen, as thecase of hydrogen purification from a H₂/CO₂ mixture, with carbon dioxidethe strongly adsorbed second component.

It will be seen from FIG. 7 that (P_(INT)−P_(L))/(P_(H)−P_(L))=0.2 atthe value 267 of the time function, at which point the equalization anddepressurization steps are each about 95% complete in approaching theterminal pressure of that step.

For identical step time intervals “t” of these steps, as is obtainedwith the cycle timing of FIGS. 5 and 6 (and also the timing of FIG. 9,but not for the timing of FIG. 4), the orifice areas “A” of orifices96-98 should therefore be approximately equal. For FIGS. 5 and 6, it maybe noted for each of the light reflux steps nominally

t=T/12,

since the step angular interval is 30°. The pressure drop resistance ofeach of the three light reflux steps should be substantially equal forthe cycle of FIGS. 5 and 6 so that the desirable pressure transientcurves of FIG. 7 will be attained with a nominal step time intervaldefined by time 267. Furthermore, equal adjustment of flow controlvalves 61-66 will not significantly upset the balance of pressurechanges between the cocurrent and countercurrent blowdown steps in FIGS.5 and 6.

Hence, the orifices 96-98 (once adjusted to approximately an equaleffective area “A”) need not be further adjustable for the cycles ofFIGS. 5 or 6, since flow control of light reflux steps can be providedby coordinated actuation of valves 61-66.

An important process embodiment of the present invention is thus toestablish equal time intervals for each of the light reflux steps(equalization, cocurrent blowdown to purge, and productrepressurization) by the porting of the second distributor valve, andthen to provide coordinated actuation of flow controls (e.g. valves 61to 66) between the second end of each bed and the second distributorvalve, so as to achieve at any operating cycle frequency of the processsubstantial completion of the pressure equalization step while avoidingexcessively rapid rate of pressure change, and while maintaining theratio

0.1<(P_(INT)−P_(L))/(P_(H)−P_(L))<0.3, or preferably

0.15<(P_(INT)−P_(L))/(P_(H)−P_(L))<0.25.

With flow control valves 61-66 fully open, and orifices 96-98 also openwith flow area “A”, the cycle of FIG. 5 can be operated at maximum cyclefrequency for the given pressure ratio P_(H)/P_(L) to achieve pressuretransient curves for the light reflux steps similar to FIG. 6. The cyclecannot be operated at higher frequency, except by lowering the pressureratio P_(H)/P_(L).

If the cycles of FIG. 5 or 6 are operated at lower frequency at the samepressure ratio PH/PL, the effective orifice flow area “A” must beadjusted in substantially inverse ratio to the step time interval “t” orcycle period “T”, so that the step time coefficient 267 is approximatelyconstant. If the cycle period were increased by e.g. a factor of twowithout adjusting the effective “A” by a factor of ½, the cocurrentblowdown would be continued too far so P_(INT) would be much too low andthe countercurrent blowdown step would be nearly eliminated, resultingin loss of purification and recovery performance for the light product.

Since the cycles of FIGS. 5 and 6 operate well with equal “A” for eachlight reflux step, it is immaterial to performance whether the effective“A” is controlled by adjusting the orifices 96-98 or the flow controls61-66. In practice, the orifices 96-98 on the rotor within the seconddistributor valve are less conveniently controlled operationally, soflow controls 61-66 have been provided for more convenient operatorcontrol access. For these cycles, operational adjustability of orifices96-98 may not be required, once the apparatus has been assembled withcorrect adjustments for a given application.

In the cycle of FIG. 4, the light reflux steps have unequal timeintervals. The duration of the cocurrent blowdown step is twice as long(T/6) as the duration of the equalization and repressurization steps.Therefore, orifice 98 throttling the countercurrent blowdown step shouldhave an effective flow area “A” (after lumped inclusion of otherpressure drops between the second ends of beds exchanging gas in lightreflux steps in the effective orifice area) only half the effectiveorifice flow area associated with orifices 97 and 96 throttling theequalization and repressurization steps respectively.

When the light reflux orifices are to be used for flow adjustment, itmay be noted that the most critical adjustment is that of orifice 98controlled countercurrent blowdown flow because maladjustment of thatorifice for any operating cycle frequency will upset the desirable valueof P_(INT), so that the countercurrent blowdown may be too large or toosmall. If P_(INT) is too high because orifice 98 is too restrictive, thecountercurrent blowdown will be relatively large while the resultingsmall cocurrent blowdown will release only a small volume of purge gas.If P_(INT) is too low because orifice 98 is too open, the countercurrentblowdown may be too small, compromising purity.

One simplification within the invention is to use fixed orifices 96 and97 on the less critical equalization and repressurization steps, whileusing an adjustable orifice 98 to regulate the more criticalcountercurrent blowdown. This approach is especially suitable for thecycle of FIG. 4, having a slow countercurrent blowdown which is moresensitive to control as has been verified in experimental prototypes ofthe invention.

The above discussed control characteristics have been verifiedexperimentally with prototypes, using six beds with valve timingaccording to FIG. 4 or FIG. 9. It was found that maladjustment of theflow controls could render the process inoperative, while satisfactoryperformance in hydrogen purification and oxygen concentrationapplications was demonstrated, with the orifices adjusted for eachoperating condition to achieve the pressure transients as depicted inFIG. 7.

FIGS. 8 and 9

FIG. 8 shows another embodiment 300 of a six bed PSA apparatus withseveral alternative features of the invention. Component numbering andnomenclature are similar to FIG. 1, except as noted below. Like FIG. 1,FIG. 8 schematically shows all bed ports and function ports of the firstand second distributor valves, and likewise does not show the geometryof the ports relative to the axis of each valve. FIG. 9 shows timingdiagrams and the pressure waveform for apparatus 300.

Apparatus 300 is configured to deliver the light product gas through thesecond distributor valve. Light product gas, enriched in the secondcomponent, is delivered by second function port 90, during the feed stepof each adsorbent bed, and by light product delivery conduit 301 tooptional light product compressor 302. Light product compressor with itsdownstream load provides means to regulate the pressure and flow of thelight product gas. To avoid undesirable pressure reduction below thehigher pressure of the light product gas, non-return valves 310-315 areprovided in parallel with each of flow control valves 61-66. Thenon-return valves enable gas enriched in the second component to flowfrom the adsorbent beds to the second distributor valve with minimalpressure loss, while light reflux gas flowing back from the seconddistributor valve to the adsorbent beds may be throttled by the flowcontrol valves 61-66.

Apparatus 300 illustrates alternative means of introducing a second feedgas, having a higher concentration in the first component than the feedgas. Instead of an external feed selector valve admitting alternatingpulses of the feed and a second feed (or heavy reflux), a second feedsupply conduit 326 introduces the second feed directly to second feedtransfer chamber 327 between rotor 40 and stator housing 38. Transferchamber 327 is isolated from feed transfer chamber 127 by rotary seal328, and communicates to second feed port 350 on valve surface 45.Second feed port 350 follows feed port 50 in the timing sequence offirst function ports 355 on first distributor valve timing diagram 360of FIG. 9. Second feed port 350 corresponds to second feed port 226 inFIG. 6.

The second feed gas is admitted to the adsorbent beds in the latterportion of the feed step, or in a second feed step as provided in FIG.6, after the admission of the feed gas less concentrated in the firstcomponent than the second feed gas. The sequential admission of feed gasincreasingly concentrated in the first component helps to provide arising concentration of the first component toward the first end of theadsorbent beds, and of the second component toward the second end of theadsorbent beds.

The process aspect here is supplying the feed gas mixture during theinitial part of high pressure step (A) to the first end of the adsorbentbed, and then supplying a second feed gas with a greater concentrationof the first component during the later part of step (A) to the firstend of the adsorbent bed.

The second feed gas may be heavy reflux gas diverted from the exhaustgas and recompressed, as discussed for the embodiment of FIG. 1.Alternatively, the second feed gas may be another gas mixture, leaner inthe second component than the first feed gas mixture. This principle mayreadily be generalized to a plurality of feed gases, each admitted inascending order of concentration in the first component or decliningorder of concentration in the second component. Thus, in hydrogenrecovery from refinery waste gases, there may be a multiplicity of feedgases with differing concentrations of hydrogen as the second component.

Apparatus 300 also includes provision in the second distributor valvefor a second equalization step of the process. An additional lightreflux withdrawal port 391 is provided, communicating through adjustableorifice 392 in rotor 80 to light reflux return port 394. The timing ofports 391 and 394 is shown in function port sequence 395 of seconddistributor valve timing diagram 396 of FIG. 9. The second equalizationstep includes depressurization of one bed from P_(EQ1) to approachP_(EQ2), exchanging light reflux gas as indicated by arrow 399 toanother bed being pressurized from P_(L) to approach P_(EQ2).

FIG. 10

As the adjustable orifices in the rotor of the second distributor valveare enclosed within a rotor and behind both dynamic and static seals,their operational adjustment presents challenges, particularly when thePSA system is purifying dangerous gases such as hydrogen. Hence theinvention provides means for their adjustment.

FIG. 10 is a schematic drawing of an alternative second distributorvalve 400 with control means for the adjustable orifices of the rotor asconfigured for embodiment 1 of FIG. 1. Adjustable orifices 96-98 areprovided as throttle valves mounted in rotor 80, each with identical orsimilar external actuation means, described here in detail foradjustable orifice 97. Light reflux withdrawal port 91 communicates byconduit 401 to upstream valve chamber 402. Chamber 402 is penetrated byvalve stem 405 with coaxial needle 406 aligned with valve seat 408. Theadjustable throttle valve orifice is defined between needle 406 and seat408, and provides fluid communication with downstream valve chamber 410which in turn communicates by conduit 412 to light reflux return port94.

Drive end 414 of valve stem 405 is isolated from process fluid by seal415, and is provided with a drive pin 416 penetrating a drive slot 417in rotor 80. Slot 417 has axial clearance for pin 416, sufficient formovement of stem 405 with needle 406 to adjust the orifice area betweenthe needle and valve seat 408. Drive pin 416 projects clear of rotor 80to roller 418 on drive pin 416, engaging circumferential thrust collar420. Thrust collar 420 is slidably mounted for axial motion concentricto axis 83 in stationary guide 421, which is a coaxially concentricextension of stator housing 78 external of rotary seal 422. Actuationpin 424 on thrust collar 420 penetrates slot 425 in guide 421, and iscoupled to linear actuator 430. Thus, linear motion of actuation pin 424by actuator 430 is directly transmitted through thrust collar 420 anddrive pin 416 to shift the valve stem.

Rotary seal 422 seals chamber 435 between rotor 80 and stator housing78. Rotor 80 has a diameter 436 greater than the sealing diameter ofrotary seal 422. Chamber 435 communicates with light reflux withdrawalport 90 so as to pressurize chamber 435 to substantially the higherpressure, thus providing gas loading means urging of rotor 80 onto valvesurface 85. Mechanical valve loading means may also be provided byspring 438 loading thrust washer 439 onto rotor 80.

FIG. 11

An alternative embodiment 450 of the second distributor valve uses fluidtransfer chambers between the rotor 80 and the stator housing 78, sothat the adjustable orifices can be provided as throttle valves externalto the stator housing.

On a common sealing diameter, rotary seals 451, 452, 453, 454 and 455mutually isolate chamber 107 communicating in rotor 80 to light refluxwithdrawal port 90 at substantially the higher pressure, transferchamber 461 communicating to light reflux return port 93, transferchamber 462 communicating to light reflux withdrawal port 91, transferchamber 463 communicating to light reflux return port 94, transferchamber 464 communicating to light reflux withdrawal port 92, andchamber 109 communicating to light reflux return port 95 atsubstantially the lower pressure. Adjustable orifice 96 is provided asthrottle valve 471 communicating through stator housing 78 to chambers107 and 461. Adjustable orifice 97 is provided as throttle valve 472communicating through stator housing 78 to chambers 462 and 463.Adjustable orifice 98 is provided as throttle valve 473 communicatingthrough stator housing 78 to chambers 464 and 109.

FIG. 12

Several refinements for providing flow control to minimize peak gas flowvelocities, or to increase the average flow velocity in each step, arenow discussed.

One such refinement is to oscillate the angular velocity of the firstrotary distributor valve, to extend its open periods. With reference toFIG. 1, FIG. 12 provides an example of first valve drive means 41 andsynchronizing linkage 152, here provided as a gear train 500 couplingmotor 155 through variable speed drive 154 to shaft 42 turning rotor 40in stator housing 38. Shaft 42 carries gear 501, driven by pinion 502 onlay shaft 503. The gear reduction ratio from shaft 503 to shaft 42 is6:1 for the example of a PSA system with six adsorbent beds, or moregenerally N:1 for N adsorbent beds in parallel. Variable speed drive 154drives output shaft 508, which is coupled to lay shaft 503 by a pair ofnoncircular or elliptical gears 505 and 506. Elliptical gears 505 and506 have the same number of teeth.

By selecting readily available elliptical gears whose maximum pitchradius is twice the minimum pitch radius, constant rotary speedoperation of shaft 508 will result in a variation of the instantaneousangular velocity of shaft 503 from half that of shaft 508 to twice thatof shaft 508, or over a range of 4:1. Hence the instantaneous angularvelocity of first rotary valve shaft 42 will also vary through a 4:1ratio, with six maxima and six minima per complete revolution.

The apparatus for “N” adsorbent beds in parallel has drive meansincluding angular velocity variation means to vary the angular velocityof the rotor of the first distributor valve at a multiple “N” times thecycle frequency, so as to extend the time interval during which afunction port is substantially fully open to each bed port, and toreduce the time interval during which that function port issubstantially closed to any bed port, while maintaining the minimumangular velocity of the rotor to be greater than zero throughout thecycle so as to avoid excessive wear due to stopping and restartingrotation. The angular velocity variation means may be provided as a pairof noncircular gears in the drive train to the first distributor valve.

The angular phase of shaft 42 with respect to the angular velocityoscillations generated by the pair of elliptical gears will be set sothat the angular velocity of rotor 80 is low while the first bed portsand first function ports are mutually opened, while the angular velocitywill be high while the ports are closed and switching. Hence, the timeduring which the valve ports are nearly fully open will be maximized,while the time during which the valve ports are closed or nearly closedwill be minimized. Since the minimum angular velocity of the rotor iswell above zero, rapid wear due to stick-slip conditions (that wouldresult from intermittent rotation with intervals of completely stoppedrotation) is avoided.

By minimizing the duration of low flow valve switching time intervals,this feature enhances productivity of the adsorbent beds and of thedistributor valve. It will be seen that the described gear train ismeans to vary the angular velocity of the valve rotor, so as to extendthe time interval during which a function port is substantially fullyopen to each bed port, and to reduce the time interval during which thatfunction port is substantially closed to any bed port, while maintaininga finite angular velocity of the rotor throughout the cycle.

It will be evident that other mechanisms could be used to vary theangular velocity of the distributor valve rotor, N times per cycleperiod, with correct phase to extend the duration of open intervals.This description has focused on the first distributor valve, whosefunction steps have an angular interval equal to the angular spacingbetween first bed ports. Oscillating the angular velocity of the seconddistributor valve is less advantageous, as some of its function stepsmay have much shorter angular interval than the bed port angularspacing. The first distributor valve typically must carry much largerflows than the second distributor valve, and hence can benefitsubstantially from the oscillatory angular velocity feature.

A further refinement is to adjust the phase relationship and angularvelocity profile, so that the distributor valve opens relatively slowlyand closes relatively quickly. This feature will provide increasedthrottling between partly open ports at the beginning of equalization,blowdown or repressurization steps. At the beginning of those steps, thedriving pressure difference is greatest, so increased throttling thencan usefully reduce peak velocities.

The principle of asymmetric throttling over the distributor valves, withstronger throttling at the beginning relative to the end ofpressurization, equalization and blowdown steps, can also be achieved byshaping the valve ports. Thus, purge exhaust port 52 of FIG. 5 is shownwith a narrow tapered leading edge 224, so that bed ports 30-35 willopen gradually to port 52 with initially a small open orifice forrelatively more intensive throttling, gradually opening to the maximumport orifice, and then after the open interval will close relativelyabruptly. It can be seen from FIG. 6 that greater throttling at theearly part of each step, progressively opening the valve ports to thefully open orifice area toward the end of the step, will make the flowmore uniform through most of the step, except at the extreme beginningand end.

Another desirable refinement in larger scale applications is to make thelands between function ports somewhat narrower than the width of the bedports, so that flow between the function port and bed ports is nevercompletely closed. With a brief time interval of each function portbeing slightly open (with substantial throttling) to two beds,cross-port leakage between beds will be small, while flow pulsations andvalve opening/closing time intervals will be reduced.

FIGS. 13 and 14

The rotary distributor valves discussed above have used gas pressure orcompression spring (e.g. mechanical spring) loading systems concentricto the valve rotary axis, to ensure close contact between the rotor andstator at the valve surface. When the valve has N bed ports and itsfunction ports spaced over 360°, so that one rotation of the rotorcorresponds to one cycle of the process, it is unbalanced (as will beevident from FIGS. 2 and 3) because the higher and lower pressurefunction ports are on opposed sides of the axis. As a result of theimbalance, high contact pressures will be established between the rotorand the stator adjacent the lower pressure function ports. Radialbalance is more important for the first distributor valve, as it istypically larger than the second distributor valve.

FIGS. 13 and 14 show an alternative embodiment 600 of the firstdistributor valve in which approximate radial balance of the contactpressure distribution on the valve surface 45 is achieved bycommunicating the pressure distribution on the valve surface to aplurality of axially aligned loading pistons 601-607 disposed in acoaxial annular ring around the axis 43 within the valve rotor at aradius approximately equal to or somewhat greater than the radius of thefunction ports. Each of the pistons 603-607 is pressurized by the localpressure at its axially projected position on the valve surface(typically corresponding to a function port), and is sealed by a pistonring 608 in a cylinder 613-617 in rotor 40, with each cylinder parallelto axis 43. The loading pistons are reacted on a rotating thrust plate620, bearing against stationary thrust pad 621 of self-lubricatingmaterial. Thrust pad 621 is supported within stator housing 38, normalto the axis of rotation. Each of the loading pistons is located by athrust socket 622 in thrust plate 620, thus forcing corotation of thethrust plate with the rotor.

FIG. 13 is a schematic drawing of valve embodiment 600, showing all ofthe bed ports and function ports, which would in fact be at a singleradius from axis 43 as shown in FIG. 14. Likewise, FIG. 13 shows all ofthe loading pistons, which would be at a single radius substantiallyidentical to or somewhat greater than the radius of the function portsfrom axis 43. FIG. 14 is section 623-624 of FIG. 13, and shows theannular pattern of the loading pistons at a somewhat greater radius andconcentric with the function ports 50, 51 and 52. At the same radius asthe function ports, pressure sensing ports 625, 626 and 627(corresponding to positions in the valve surface lacking a functionport) are positioned at 60° spacing from each other or from adjacentfunction port centers. Port 51 communicates to countercurrent blowdownflow control valve 132 via conduit 131 and transfer chamber 130, and byconduit 631 to cylinder 613. Port 625 communicates by conduit 634 tocylinder 614. Port 50 communicates by conduit 635 to cylinder 615, andto feed supply conduit 126 via transfer chamber 127. Port 626communicates by conduit 636 to cylinder 616. Port 627 communicates byconduit 637 to cylinder 617. Purge exhaust port 52 communicates byconduit 640 to blank cylinder 641, communicating with chamber 642between the rotor and the thrust plate 610, and thence to exhaustconduit 121, which by conduit 643 vents annular chamber 644 between thestator 36 and seal 112. No piston is needed in cylinder 641, since thatcylinder is vented to the lower pressure.

Embodiment 600 of the first distributor valve is energized by theexternally imposed pressure difference between the higher pressure inconduit 126 and the lower pressure in conduit 121. The axial thrust loadexerted by the ring of annular pistons approximately balances thepressure distribution on the valve surface, so that excessively highcontact pressures can be avoided.

FIG. 15

Another embodiment 700 of the distributor valves, here illustrated for afirst distributor valve, uses a single eccentric loading device toachieve approximate radial balance of the rotor, while balancing thestator using loading pistons analogous to those used in the rotor ofembodiment 600. Components common to first distributor valve 37 of FIG.1 are denoted with equivalent reference numerals.

Valve embodiment 700 is shown in cross section, taken across the planeof bed conduits 20 and 23 connecting bed port 30 and 33 respectively tobeds 2 and 5, which are not shown. Sealing connections between each ofthe bed conduits in housing 38 and corresponding bed ports in stator 36are provided by fluid transfer sleeves, with fluid transfer sleeves 710and 713 shown respectively for bed ports 30 and 33. The fluid transfersleeves are sealed in the housing and stator by static seals 720 and721. Compression springs 730 may optionally be provided to urge thefluid transfer sleeves toward the stator. The fluid transfer sleevesengage the stator against rotation relative to housing 38.

It will be evident that each fluid transfer sleeve exerts an axialthrust on the stator, corresponding to the pressure in that bed portacting on the axial area of each fluid transfer sleeve, plus thecompression spring forces. Hence, the set of fluid transfer sleeves actlike the loading pistons of embodiment 600, thrusting the stator toengage in sealing contact on sealing valve surface 45 against rotor 40.The force distribution will reflect the asymmetric pressure distributionin the bed ports at any instant, and will thus achieve partial balancewith the pressure distribution across face 45.

Rotor 40 is rotated by shaft 42, sealed by shaft seal 116 with sealbushing 740. Thrust loads on rotor 40 from the pressure distribution onthe valve surface 45 are reacted by a thrust slipper 750 against thrustplate 751 mounted on housing closure 752. The thrust slipper 750 is partof the rotor assembly. Thrust slipper 750 is enabled to move axially tocontact thrust plate 751 by sliding or flexing of seal means 756 (whichmay be a piston ring seal, or a flexing diaphragm or bellows); and isthereby sealed to rotor 40, and is also urged against thrust plate 751by compression spring 757 (which may be a metallic coil spring or anelastomeric spring, in the latter case possibly integral with a flexingdiaphragm seal 756).

Feed port 50 on rotor 40 communicates to chamber 758 interior to thrustslipper 750, while exhaust port 52 communicates to interior chamber 759of housing 38 external to piston 750. Chamber 758 communicates throughthe thrust plate 751 and end closure 752 to high pressure feed port 126,while chamber 759 communicates through housing 38 to low pressureexhaust port 121. Thrust plate 751 is secured to end closure 752 bydowels 761 and seal 762. End closure 752 is attached to housing 38 bycapscrews 763.

Thrust slipper 750 acts as fluid transfer means to convey feed fluidfrom the stationary housing to the rotor. The thrust slipper also loadsthe rotor against the valve surface 45, and hence the diameter of thrustslipper seal 756 must be sufficient to provide an effective pistonenergized by feed pressure in chamber 758 for positive sealing of thevalve surface. With the thrust slipper eccentrically positioned as shownin FIG. 15, radially offset from axis 43 so as to load the valve rotortoward the high pressure feed port and away from the low pressureexhaust port, approximate balance can be obtained of the presentdistribution in the valve surface. This feature allows the valve to beloaded less heavily than would otherwise be necessary, and thus tooperate with smaller internal forces, and with less frictional powerloss and heat dissipation.

It is within the scope of the invention to mount thrust slipperconcentrically to axis 43. The concentric configuration requires asomewhat larger thrust force (e.g. greater diameter of thrust slipperseal 756) to ensure positive sealing in valve surface 45, and rotor 40is subject to a greater radial force to be reacted by bushing 740 orother radial bearing.

The clearance space 770 between stator 36, housing 38 and the fluidtransfer sleeves may be used as a fluid flow passage, e.g. ofcountercurrent blowdown gas, in order to achieve enhanced convectivecooling of the valve stator and sealing surface.

It will be seen that loading means to establish fluid sealing contactbetween the rotor and stator is provided by axially aligned fluidtransfer sleeves sealing each bed port of the stator and providing fluidcommunication to the corresponding adsorbent bed of each bed port, withthe fluid transfer sleeves having enough axially projected area withoptional assistance of compression springs, so as to thrust the statoragainst the rotor. Alternative or supplementary loading means toestablish fluid sealing contact between the rotor and stator areprovided by a thrust slipper engaged by axially compliant sealing meansto the valve rotor so as to define a chamber pressurized by feed fluidto thrust the rotor against the valve sealing surface.

FIG. 16

Referring back to the embodiment of FIG. 1, flow controls 61 to 66 areadjusted by controller 164 if these flow controls or adjustable orificesare provided as throttle valves, and are to be adjusted continuouslywhile the apparatus is operating, they should be actuated simultaneouslyso that these flow controls present substantially identical orificerestrictions to light reflux gas flow at any time. Hence, the flowcontrols 61 to 66 may be ganged together mechanically for simultaneousactuation by controller 164.

FIG. 16 shows a simplified embodiment 800 in which flow controls 61 to66 are adjustable only between two discrete settings. This discretelyadjustable flow control is illustrated for flow control 61, it beingunderstood that the identical device would be applied to flow controls62 to 66. The adjustable orifice of flow control 61 has a morerestrictive setting defined by fixed orifice 801, and a less restrictivesetting defined by the combination in parallel of fixed orifices 801 and802. Orifices 801 and 802 are respectively in conduits 803 and 804branching in parallel between conduit 55 and second end 14 of bed 2. Atwo-way selector valve 805 in conduit 804 is actuated by controller 164.When selector valve 805 is open or closed, flow control 61 isrespectively at its less or more restrictive setting. With similartwo-way selector valves in each of the discretely adjustable flowcontrols 61 to 66 to switch these flow controls between substantiallyidentical more and less restrictive settings, and simultaneous actuationby controller 164 of all six selector valves, a simplified control isachieved compared to the alternative coordinated actuation ofcontinuously adjustable throttle valves.

The use of two discrete settings for flow controls 61 to 66 will beparticularly suitable for applications in which a two speed drive 154 ormotor 155 is used to operate the rotary distributor valves at two cyclefrequencies. The less restrictive setting of the flow controls would beused at the higher cycle frequency. For a wide range of flow controladjustment, more than two settings may be provided by providingadditional orifices in parallel.

It will be appreciated that the above described device of discretelyadjustable flow controls or adjustable orifices, with two or possiblymore discrete settings established by selector valves opening andclosing supplemental orifices in parallel, may be applied to any of theflow controls in the present invention, including flow controls 61 to66; adjustable orifices 96, 97 and 98; or flow control valve 132.

INDUSTRIAL APPLICABILITY

The present invention is applicable to hydrogen separation, airseparation, and to many other gas or vapour separations. The inventionovercomes barriers to the technical simplification and economic scale-upof highly efficient and productive gas separation equipment.

An important application is hydrogen recovery from refinery offgases orlow BTU syngas. PSA has previously been applied most successfully topurification of hydrogen from hydrogen rich feed streams (such as highBTU syngas generated by steam reforming of methane), typically availableat high pressure. PSA has not previously been found economic forrecovery of hydrogen from lean or very low pressure feed streams. Demandfor hydrogen is rapidly increasing in the petroleum refining industry,while that industry continues to burn large amounts of hydrogen in wastefuel gas streams.

The present invention has been tested experimentally for purification ofhydrogen generated by steam reforming of methanol or partial oxidationof methane, and for hydrogen recovery from refinery hydrotreateroffgases as well as from tail gas of conventional PSA systems.

A small industrial pilot plant according to the embodiment of FIG. 1 hasbeen operated with a methanol reformer to produce hydrogen of 99.999%purity at flow rates sufficient for a 6 kilowatt fuel cell. A variablespeed drive was used to operate the rotary distributor valves. Using theflow controls of FIG. 1, satisfactory operation was established withvarying methanol reformate feed flow and pressure over a 4:1 range ofcycle frequencies.

The present invention enables the use of simple multiport rotarydistributor valves and cooperating flow controls, with adsorbent bedscycled at relatively high frequency, to recover hydrogen from lean andlow pressure petroleum refinery offgases.

Typical application objectives are to recover hydrogen from ahydrotreater purge gas containing 30% hydrogen, supplied at a pressureof 8 atmospheres, while discharging tail gas depleted of hydrogen at 2atmospheres total pressure. With adsorbent beds approximately 1.5 metersdeep, containing 8/12 mesh pellets of suitable adsorbent (e.g. 13Xzeolite, with a guard layer of alumina dessicant at the first end of theadsorbent beds), it is found that the apparatus of the invention candeliver high purity hydrogen at cycle periods of 20 to 30 seconds. Highcycle frequency enables low adsorbent inventory. Having relativelyshallow adsorbent beds, this apparatus can be delivered to anapplication site as a fully assembled modular skid. The small adsorbentinventory and simplified controls enable competitive performance andeconomics.

The invention may also be applied to concentrate oxygen from atmosphericair, using a zeolite adsorbent on which nitrogen is more readilyadsorbed than oxygen at ambient temperature. The higher pressure of theprocess will be above atmospheric, and the lower pressure may beatmospheric or subatmospheric. Suitable adsorbents include zeolite 13Xor 10X. The typically six bed cycles of the present invention achievehigher product recovery than conventional PSA or VSA air separationcycles, while high cycle frequency again enables a low adsorbentinventory.

It will be understood that the different aspects of the presentinvention may be expressed with much diversity and in many combinationsother than the specific examples described above, under the scope of thefollowing claims.

1. Process for separating first and second components of a feed gasmixture, the first component being more readily adsorbed under increaseof pressure relative to the second component which is less readilyadsorbed under increase of pressure over an adsorbent material, suchthat a gas mixture of the first and second components contacting theadsorbent material is relatively enriched in the first component at alower pressure and is relatively enriched in the second component at ahigher pressure when the pressure is cycled between the lower and higherpressures at a cyclic frequency of the process defining a cycle period;providing for the process a number “N” of substantially similaradsorbent beds of the adsorbent material, with said adsorbent bedshaving first and second ends; and further providing for the process afirst rotary distributor valve connected in parallel to the first endsof the adsorbent beds and a second rotary distributor valve connected inparallel to the second ends of the adsorbent ends, with flow controlscooperating with the first and second distributor valves; introducingthe feed gas mixture at substantially the higher pressure to the firstdistributor valve; and rotating the first and second distributor valvesso as to perform in each adsorbent bed the sequentially repeated stepswithin the cycle period of: (A) supplying a flow of the feed gas mixtureat the higher pressure through the first distributor valve to the firstend of the adsorbent bed during a feed time interval, withdrawing gasenriched in the second component from the second end of the adsorbentbed, and delivering a portion of the gas enriched in the secondcomponent as a light product gas, (B) withdrawing a flow of gas enrichedin the second component as light reflux gas from the second end of theadsorbent bed through the second distributor valve, so as todepressurize the adsorbent bed from the higher pressure toward anequalization pressure less than the higher pressure, while controllingthe flow so that the pressure in the bed approaches the equalizationpressure within an equalization time interval, (C) withdrawing a flow oflight reflux gas enriched in the second component from the second end ofthe adsorbent bed through the second distributor valve, so as todepressurize the adsorbent bed from approximately the equalizationpressure to an intermediate pressure less than the equalization pressureand greater than the lower pressure, while controlling the flow so thatthe pressure in the bed reaches approximately the intermediate pressurewithin a cocurrent blowdown time interval, (D) withdrawing a flow of gasenriched in the first component from the first end of the adsorbent bedthrough the first distributor valve, so as to depressurize the adsorbentbed from approximately the intermediate pressure to approach the lowerpressure, while controlling the flow so that the pressure in the bedapproaches the lower pressure within a countercurrent blowdown timeinterval, (E) returning a low of light reflux gas enriched in the secondcomponent from the second distributor valve to the second end of theadsorbent bed at substantially the lower pressure, while withdrawing gasenriched in the first component from the first end of the adsorbent bedand through the first distributor valve over a purge time interval, saidflow of gas enriched in the second component from the second distributorvalve being withdrawn from another of the adsorbent beds which isundergoing cocurrent blowdown step (C) of the process, (F) returning aflow of light reflux gas enriched in the second component from thesecond distributor valve to the bed, so as to repressurize the adsorbentbed from approximately the lower pressure to approach the equalizationpressure, while controlling the flow so that the pressure in the bedapproaches the equalization pressure within an equalization timeinterval, said flow of gas enriched in the second component from thesecond distributor valve being withdrawn from another of the adsorbentbeds which is undergoing equalization step (B) of the process, (G)admitting gas to the adsorbent bed, so as to further repressurize theadsorbent bed from the equalization pressure toward the higher pressure,while controlling the flow so that the presence in the bed approachesthe higher pressure within a repressurization time interval, (H)cyclically repeating steps (A) to (G).
 2. The process of claim 1,further varying cycle frequency so as to achieve desired purity,recovery and flow rate of the light product gas.
 3. The process of claim1, in step (G) returning a flow of light reflux gas enriched in thesecond component from the second distributor valve to the bed, so as torepressurize the adsorbent bed to approach the higher pressure, whilecontrolling the flow so that the pressure in the bed approaches thehigher pressure within a repressurization time interval, the flow of gasenriched in the second component from the second distributor valve beingwithdrawn from another of the adsorbent beds which is undergoing feedstep (A) of the process.
 4. The process of claim 1, in step (G)admitting feed gas from the first distributor valve to the bed, so as torepressurize the adsorbent bed to approach the higher pressure, whilecontrolling the flow so that the pressure in the bed approaches thehigher pressure within a repressurization time interval.
 5. The processof claim 1, supplying the feed gas mixture during the initial part ofstep (A) to the first end of the adsorbent bed, and then supplying asecond feed gas with a greater concentration of the first componentduring the later part of step (A) to the first end of the adsorbent bed.6. The process of claim 5, recompressing a portion of the gas enrichedin the first component withdrawn from the first end of an adsorbent bedduring step (D) or preferably (E) to substantially the higher pressure,and supplying this portion of the gas enriched in the first component asthe second feed gas through the first distributor valve to the first endof the adsorbent bed in the latter part of the feed time interval instep (A).
 7. The process of claim 6, providing a feed selector valve toalternatingly direct the feed gas mixture or the heavy reflux gasthrough the first distributor valve to the first end of the adsorbentbed, and switching the feed selector valve at a frequency “N” times thecycle frequency.
 8. The process of claim 1, exchanging light reflux gasenriched in the second component between a bed undergoing step (B) andanother bed undergoing step (F) directly through the second distributorvalve in substantially identical equalization time intervals for thosesteps (B) and (F).
 9. The process of claim 8, in which the cycle periodis approximately the sum of the feed time interval, twice theequalization time interval, the cocurrent blowdown time interval, thepurge time interval, and the repressurization time interval.
 10. Theprocess of claim 1, further providing adjustable orifices interposedbetween the second end of each adsorbent bed and the second distributorvalve as flow controls cooperating with the second distributor valve,one adjustable orifice being provided for each bed and the orificesbeing adjusted simultaneously so as to have substantially identicalsettings at any time, and adjusting the orifices so as to control theflow at the second ends of the adsorbent beds in steps (B), (C), (E),(F) and (G).
 11. The process of claim 10, further providing a productdelivery check valve for each adsorbent bed communicating from thesecond end of that adsorbent bed to a light product manifold, anddelivering the light product through the product delivery check valves.12. The process of claim 10, in which the time intervals of steps (B),(C) and (F) are substantially equal, so that the intermediate pressureremains substantially constant as the orifices are adjusted.
 13. Theprocess of claim 10, in which the orifices are adjusted by switchingbetween discrete settings.
 14. The process of claim 1, furtherdelivering the light product gas through the second distributor valve.15. The process of claim 1, further providing an adjustable orifice inthe second distributor valve as a flow control cooperating with thesecond distributor valve, and adjusting the orifice so as to control theflow in step (C).
 16. The process of claim 1, further providingadjustable orifices in the second distributor valve as flow controlscooperating with the second distributor valve, and adjusting theorifices so as to control the flow at the second ends of the adsorbentbeds in steps (B), (C), (E), (F) and (G).
 17. The process of claim 1,further providing a flow control cooperating with the first distributorvalve to control the flow in step (D) so as to establish theintermediate pressure relative to the higher and lower pressures, suchthat the ratio of the difference between the intermediate pressure andthe lower pressure to the difference between the higher pressure and thelower pressure is in the range of approximately 0.15 to 0.25.
 18. Theprocess of claim 1, further controlling the flow in step (A) byestablishing the volumetric flow of the feed gas mixture at the higherpressure.
 19. The process of claim 1, further controlling the flow instep (A) by regulating the pressure at which the product gas iswithdrawn.
 20. The process of claim 1, further controlling the flow ineach step so as to avoid damaging the adsorbent by transient high flowvelocity in the adsorbent bed.
 21. The process of claim 1, furthercontrolling the flow velocities in steps (B), (C), (D), (F) and (G) sothat the ratio of the peak flow velocity to the average flow velocity inthose steps will not exceed approximately 2:1.
 22. Apparatus forseparating first and second components of a feed gas mixture, the firstcomponent being more readily adsorbed under increase of pressurerelative to the second component which is less readily adsorbed underincrease of pressure over an adsorbent material, such that a gas mixtureof the first and second components contacting the adsorbent material isrelatively enriched in the first component at a lower pressure and isrelatively enriched in the second component at a higher pressure whenthe pressure is cycled between the lower and higher pressures at acyclic frequency of the process defining a cycle period, the apparatusincluding (a) a number “N” of substantially similar adsorbent beds ofthe adsorbent material, with said adsorbent beds having first and secondends defining a flow path through the adsorbent material; (b) lightproduct delivery means to deliver a light product flow of gas enrichedin the second component from the second ends of the adsorbent beds; (c)a first rotary distributor valve connected in parallel to the first endsof the adsorbent beds; the first distributor valve having a stator and arotor rotatable about an axis; the stator and rotor comprising a pair ofrelatively rotating valve elements, the valve elements being engaged influid sealing sliding contact in a valve surface, the valve surfacebeing a surface of revolution coaxial to the axis, each of the valveelements having a plurality of ports to the valve surface and insequential sliding registration with the ports in the valve surface ofthe other valve element through the relative rotation of the valveelements; one of said valve elements being a first bed port elementhaving N first bed ports each communicating to the first end of one ofthe N adsorbent beds; and the other valve element being a first functionport element having a plurality of first function ports including a feedport, a countercurrent blowdown port and a purge exhaust port; with thebed ports spaced apart by equal angular separation between adjacentports; and with the first function ports and first bed ports at the sameradial and axial position on the valve surface so that each firstfunction port is opened in sequence to each of the N first bed ports byrelative rotation of the valve elements; (d) a second rotary distributorvalve connected in parallel to the second ends of the adsorbent beds andcooperating with the first distributor valve; the second distributorvalve having a stator and a rotor rotatable about an axis; the statorand rotor comprising a pair of relatively rotating valve elements, thevalve elements being engaged in fluid sealing sliding contact in a valvesurface, the valve surface being a surface of revolution coaxial to theaxis, each of the valve elements having a plurality of ports to thevalve surface and in sequential sliding registration with the ports inthe valve surface of the other valve element through the relativerotation of the valve elements; one of said valve elements being asecond bed port element having N second bed ports each communicating tothe second end of one of the N adsorbent beds; and the other valveelement being a second function port element having a plurality ofsecond function ports including a plurality of light reflux withdrawalports and light reflux return ports, with each light reflux return portcommunicating through the second function element to a light refluxwithdrawal port; with the bed ports spaced apart by equal angularseparation between adjacent ports; and with the function ports and bedports at the same radial and axial position on the valve surface so thateach function port is opened in sequence to each of the N bed ports byrelative rotation of the valve elements; (e) drive means to establishrotation of the rotors, and hence relative rotation of the bed portelements and the function port elements of the first and seconddistributor valves, with a phase relation between the rotation of therotors and angular spacing of the function ports of the first and seconddistributor valves so as to establish for each adsorbent bedcommunicating to corresponding first and second bed ports the followingsequential and cyclically repeated steps at a cycle frequency for thosebed ports; (i) the first bed port is open to the feed port, while lightproduct gas is delivered by a light product delivery means, (ii) thesecond bed port is open to a light reflux withdrawal port, (iii) thefirst bed port is open to the countercurrent blowdown port, (iv) thefirst bed port is open to the purge exhaust port, while the second bedport is open to a light reflux return port; (f) countercurrent blowdownflow control means cooperating with the first distributor valve; (g)light reflux flow control means cooperating with the second distributorvalve; (h) feed supply means to introduce the feed gas mixture to thefeed port of the first distributor valve at substantially the higherpressure; and (i) exhaust means to remove gas enriched in the firstcomponent from the purge exhaust port of the first distributor valve.23. The apparatus of claim 22, in which the second function ports of thesecond distributor valve include light reflux withdrawal ports towithdraw light reflux gas enriched in the second component from bedsundergoing feed, equalization depressurization and cocurrent blowdownsteps; light reflux return ports to supply gas enriched in the secondcomponent to beds undergoing purge, equalization pressurization andrepressurization steps; and each light reflux withdrawal portcommunicates to a light reflux return port through an orifice; so as toestablish by rotation of the distributor valve rotors the followingsequential and cyclically repeated steps for the adsorbent bed of: (A)the first bed port is open to the feed port, while the second bed portis open to a light reflux withdrawal port communicating through anorifice to a light reflux return port open to repressurize another bedundergoing step (F) below, and light product gas is delivered from thesecond end of the adsorbent bed by a light product delivery valve; (B)the second bed port is open for pressure equalization to a light refluxwithdrawal port communicating through an orifice to a light reflux portopen to another bed undergoing step (F) below, so as to equalize thepressures of the beds; (C) the second bed port is open forcountercurrent blowdown to a light reflux withdrawal port communicatingthrough an orifice to a light reflux port open for purging to anotherbed undergoing step (E) below; (D) the first bed port is open to thecountercurrent blowdown port, so as to depressurize the bed to the lowerpressure; (E) the first bed port is open to the purge exhaust port,while the second bed port is open to a light reflux return port so as toreceive light reflux gas from another bed undergoing step (C) above; (F)the second bed port is open to a light reflux return port so as toreceive light reflux gas from another bed undergoing step (B) above forpressure equalization; and (G) the second bed port is open to a lightreflux return port so as to receive light reflux gas from another bedundergoing step (A) above for repressurization.
 24. The apparatus ofclaim 23, in which the first bed port is opened to the feed port beforelight product gas is delivered from the second end of the adsorbent bedby the light product delivery valve, so that repressurization of theadsorbent bed is achieved at least in part by feed gas.
 25. Theapparatus of claim 23, in which each light reflux withdrawal portcommunicates to a light reflux return port through an orifice which isan adjustable orifice, provided as light reflux flow control means. 26.The apparatus of claim 23, in which the first bed port element is thestator, and the first function port element is the rotor, of the firstdistributor valve; and the second bed port element is the stator, andthe second function port element is the rotor, of the second distributorvalve.
 27. The apparatus of claim 26, in which each light refluxwithdrawal port communicates to a light reflux return port through anorifice which is an adjustable orifice within the rotor, provided aslight reflux flow control means.
 28. The apparatus of claim 26, withactuator means to control the adjustable orifice from outside the rotorwhile the rotor is revolving.
 29. The apparatus of claim 28, in whichthe adjustable orifice is provided as a throttle valve within the rotor,and the actuator means is coupled to the throttle valve through amechanical linkage.
 30. The apparatus of claim 26, in which each lightreflux withdrawal port communicates to a light reflux return portthrough an adjustable orifice which is a throttle valve external to therotor, with transfer chambers having rotary seals providing fluidcommunication between the throttle valve and the light reflux withdrawalport, and between the throttle valve and the light reflux return port.31. The apparatus of claim 26, in which the light reflux control meansincludes an adjustable orifice or throttle valve interposed between thesecond end of each adsorbent bed and the second distributor valve, andmeans to adjust the orifices or throttle valves simultaneously such thateach of the adjustable orifices will have substantially identicalsettings at each time.
 32. The apparatus of claim 31, in which each ofthe adjustable orifices is provided by at least two fixed orifices inparallel, with one of the fixed orifices always open to flow, andanother orifice being opened or closed to flow by a selector valve so asto establish respectively less restrictive and more restrictive discretesettings of the adjustable orifice.
 33. The apparatus of claim 31, inwhich the light product delivery means for each adsorbent bed isprovided as a check valve enabling flow from the second end of thatadsorbent bed to a product delivery manifold.
 34. The apparatus of claim31, in which the light product delivery means is the second distributorvalve, provided with a light product delivery port; and a check valve isprovided in parallel with each adjustable orifice or throttle valve soas to permit unrestricted flow from the second end of each bed to thesecond distributor valve.
 35. The apparatus of claim 22, with the drivemeans being a variable speed drive controlled by a cycle frequencycontroller.
 36. The apparatus of claim 22, with the drive meansincluding angular velocity variation means to vary the angular velocityof the rotor of the first distributor valve at a multiple “N” times thecycle frequency, so as to extend the time interval during which afunction port is substantially fully open to each bed port, and toreduce the time interval during which that function port issubstantially closed to any bed port, while maintaining the minimumangular velocity of the rotor during the cycle to be greater than zero.37. The apparatus of claim 36, in which the angular velocity variationmeans is provided as a pair of noncircular gears in the drive train tothe first distributor valve.
 38. The apparatus of claim 22, in which afunction port is shaped so as to provide a gradually opening orifice soas to impose relatively intensive throttling at the beginning of ablowdown, pressurization or equalization step.
 39. The apparatus ofclaim 22, in which the valve surface of a distributor valve is a flatdisc normal to the axis of that valve, and with loading means toestablish fluid sealing sliding contact between the stator and rotor ofthat distributor valve.
 40. The apparatus of claim 39, in which theloading means is in part provided by compression springs.
 41. Theapparatus of claim 39, in which the loading means includes a pluralityof axially aligned loading pistons disposed in a coaxial annulus withinthe valve rotor at substantially the radius of the function ports, witheach piston communicating to the local gas pressure at its axiallyprojected position in the valve surface, and the pistons reactingagainst a rotating thrust plate so as to achieve approximate radialbalance.
 42. The apparatus of claim 39, in which the loading means toestablish fluid sealing contact between the rotor and stator is providedby axially aligned fluid transfer sleeves for each bed port of thestator and providing sealed fluid communication to the correspondingadsorbent bed of each bed port, with the fluid transfer sleeves havingenough axially projected area so as to thrust the stator against therotor in sealing contact, with optional assistance of compressionsprings.
 43. The apparatus of claim 42, in which a clearance spacebetween stator and the fluid transfer sleeves may be used as a fluidflow passage to achieve enhanced convective cooling of the valve. 44.The apparatus of claim 39, in which the loading means to establish fluidsealing contact between the rotor and stator is provided by a thrustslipper reacting against a stationary thrust plate and engaged byaxially compliant sealing means to the valve rotor so as to define achamber pressurized by feed fluid to thrust the rotor against the valvesealing surface.
 45. The apparatus of claim 44, in which the thrustslipper provides fluid transfer means to convey feed fluid from astationary housing to the rotor.
 46. The apparatus of claim 44, in whichthe thrust slipper is eccentrically positioned and radially offset fromthe axis of said rotor toward the high pressure feed port and away fromthe low pressure exhaust port, so as to balance approximately thepressure distribution in the valve sealing surface.
 47. A rotarydistributor valve comprising: a stator housing having a stator housingface, wherein the stator housing face comprises at least three fluidport openings, and a central axis of rotation; a rotor having a rotorface, wherein the rotor face comprises at least two fluid port openingsand a central axis of rotation disposed coaxially with the axis ofrotation of the stator housing face; an intermediate valve elementhaving first and second faces, a central axis of rotation disposedcoaxially with the axes of rotation of the stator housing and rotorfaces, and a plurality of fluid ports extending between the first andsecond faces, which fluid ports are aligned with the fluid port openingsin one of the stator housing face or the rotor face, wherein the firstface of the intermediate valve element faces the rotor face and is influidly sealing contact with the rotor face, and the second face of theintermediate valve element faces the stator housing face and is influidly sealing contact with the stator housing face; and loading meansoperable to exert a sealing force on the rotary valve, which urges thestator housing face and the rotor face towards each other to promotefluidly sealing contact between the rotor and stator housing faces andthe first and second faces of the intermediate valve elementrespectively; wherein the stator housing face and the rotor face arerotatable relative to each other about their common coaxial axis ofrotation; wherein the rotor additionally comprises at least one fluidpassage connecting a first fluid port opening in the rotor face to asecond fluid port opening in the rotor face; and wherein the loadingmeans comprises gas pressure loading means, and the gas pressure loadingmeans is operable to exert distributed variable sealing force around asealing face of the rotary distributor valve, said distributed variablesealing force being responsive to the distribution of pressure in thefluid port openings in the stator housing face.
 48. A rotary distributorvalve comprising: a stator housing having a stator housing face, whereinthe stator housing face comprises at least three fluid port openings,and a central axis of rotation; a rotor having a rotor face, wherein therotor face comprises at least two fluid port openings and a central axisof rotation disposed coaxially with the axis of rotation of the statorhousing face; and an intermediate valve element having first and secondfaces, a central axis of rotation disposed coaxially with the axes ofrotation of the stator housing and rotor faces, and a plurality of fluidports extending between the first and second faces, which fluid portsare aligned with the fluid port openings in one of the stator housingface or the rotor face, wherein the first face of the intermediate valveelement faces the rotor face and is in fluidly sealing contact with therotor face, and the second face of the intermediate valve element facesthe stator housing face and is in fluidly sealing contact with thestator housing face; wherein the stator housing face and the rotor faceare rotatable relative to each other about their common coaxial axis ofrotation; wherein the rotor additionally comprises at least one fluidpassage connecting a first fluid port opening in the rotor face to asecond fluid port opening in the rotor face; and wherein the rotoradditionally comprises flow control means to control fluid flow withinthe at least one fluid passage.
 49. The rotary distributor valveaccording to claim 47 wherein the intermediate valve comprises a statorsecured to the stator housing face.
 50. The rotary distributor valveaccording to claim 47 wherein the intermediate valve element fluid portsare aligned with the fluid port openings in the stator housing face, andthe intermediate valve element remains rotationally stationary relativeto the stator housing face during relative rotation of the statorhousing face and the rotor face.
 51. The rotary distributor valveaccording to claim 47 additionally comprising rotary drive meansoperable to rotate the rotor face and stator housing face relative toeach other.
 52. The rotary distributor valve according to claim 51wherein the rotary drive means is operable to vary the speed of relativerotation between the rotor face and stator housing face.
 53. The rotarydistributor valve according to claim 47 wherein the stator housing faceand rotor face comprise metal materials, and the intermediate valveelement comprises polymeric or carbon materials.
 54. The rotarydistributor valve according to claim 47 wherein the valve is a rotarypressure swing adsorption distributor valve.
 55. The rotary pressureswing adsorption distributor valve according to claim 54 additionallycomprising flow control means to control fluid flow within the at leastone fluid passage.
 56. The rotary pressure swing adsorption distributorvalve according to claim 55 additionally comprising rotary drive meansoperable to rotate the rotor face and stator housing face relative toeach other.
 57. The rotary pressure swing adsorption distributor valveaccording to claim 56 wherein the rotary drive means is operable to varythe speed of relative rotation between the rotor face and stator housingface.
 58. The rotary pressure swing adsorption distributor valveaccording to claim 56 additionally comprising loading means operable toexert a sealing force on the rotary valve, which urges the statorhousing face and the rotor face towards each other to promote fluidlysealing contact between at least one of the rotor and stator housingfaces and the first and second faces of the intermediate valve elementrespectively.
 59. The rotary pressure swing adsorption distributor valveaccording to claim 56 wherein the intermediate valve comprises a statorsecured to the stator housing face.
 60. The rotary pressure swingadsorption distributor valve according to claim 56 wherein theintermediate valve element fluid ports are aligned with the fluid portopenings in the stator housing face, and the intermediate valve elementremains rotationally stationary relative to the stator housing faceduring relative rotation of the rotor face and stator housing face. 61.The rotary distributor valve according to claim 60 wherein theintermediate valve element is fixedly attached to the stator housingface.
 62. The rotary pressure swing adsorption distributor valveaccording to claim 56 wherein the stator housing face, rotor face andfirst and second intermediate valve element faces are configured assurfaces of revolution.
 63. The rotary pressure swing adsorptiondistributor valve according to claim 62 wherein the stator housing face,rotor face and first and second intermediate valve element faces areconfigured as discs.
 64. The rotary pressure swing adsorptiondistributor valve according to claim 63 wherein the intermediate valveelement is a plate.
 65. A rotary distributor valve comprising: a statorhousing having a stator housing face, wherein the stator housing facecomprises at least three fluid port openings, and a central axis ofrotation; a rotor having a rotor face, wherein the rotor face comprisesat least two fluid port openings and a central axis of rotation disposedcoaxially with the axis of rotation of the stator housing face; anintermediate valve element having first and second faces, a central axisof rotation disposed coaxially with the axes of rotation of the statorhousing and rotor faces, and a plurality of fluid ports extendingbetween the first and second faces, which fluid ports are aligned withthe fluid port openings in one of the stator housing face or the rotorface, wherein the first face of the intermediate valve element faces therotor face and is in fluidly sealing contact with the rotor face, andthe second face of the intermediate valve element faces the statorhousing face and is in fluidly sealing contact with the stator housingface; wherein the stator housing face and the rotor face are rotatablerelative to each other about their common coaxial axis of rotation;wherein the rotor additionally comprises at least one fluid passageconnecting a first fluid port opening in the rotor face to a secondfluid port opening in the rotor face; wherein the valve is a rotarypressure swing adsorption distributor valve; flow control means tocontrol fluid flow within the at least one fluid passage; rotary drivemeans operable to rotate the rotor face and stator housing face relativeto each other; and loading means operable to exert a sealing force onthe rotary valve, which urges the stator housing face and the rotor facetowards each other to promote fluidly sealing contact between at leastone of the rotor and stator housing faces and the first and second facesof the intermediate valve element respectively; wherein the loadingmeans comprises distributed gas pressure loading means, the statorhousing face and rotor face each comprise at least six fluid portopenings, the intermediate valve element comprises at least six fluidports, and the rotary drive means comprises an electric rotary drivemotor.
 66. The rotary pressure swing adsorption distributor valveaccording to claim 65 wherein the electric rotary drive motor is avariable speed electric rotary drive motor.
 67. The rotary pressureswing adsorption distributor valve according to claim 66, wherein thestator housing face and rotor face comprise metal materials, and theintermediate valve element comprises at least one polymeric material.68. The rotary pressure swing adsorption distributor valve according toclaim 67 wherein the intermediate valve element comprises at least onecarbon material.